Patent Application
20120064355
The present invention relates to a multilayer lignocellulose-containing molding as defined in the claims.
Furthermore, the present invention relates to a process for the production of a multilayer lignocellulose-containing molding and the use of a multilayer lignocellulose-containing molding for the production of articles of all types and in the construction sector and for the production of pieces of furniture and furniture parts, of packaging materials, in house building or in interior finishing or in motor vehicles.
Materials based on lignocellulose are known. Important examples of lignocellulose-containing materials are wood parts, such as wood layers, wood strips, wood chips or wood fibers, it being possible for the wood fibers, optionally, also to originate from wood fiber-containing plants, such as flax, hemp, sunflowers, Jerusalem artichoke or rape. Starting materials for such wood parts or wood particles are usually timbers from the thinning of forests, residual industrial timbers and used timbers and wood fiber-containing plants.
The processing to give the desired lignocellulose-containing materials, such as wood particles, is effected by known processes, cf. for example M. Dunky, P. Niemt, Holzwerkstoffe and Leime, pages 91-156, Springer Verlag Heidelberg, 2002.
Lignocellulose-containing moldings, also referred to as woodbase materials here in the case of wood as lignocellulose, are an economical and resource-protecting alternative to solid wood and have become very important, particularly in furniture construction and as building materials. As a rule, wood layers of different thickness, wood strips, wood chips or wood fibers of various timbers serve as starting materials for woodbase materials. Such wood parts or wood particles are usually pressed at elevated temperature with natural and/or synthetic binders and, optionally, with addition of further additives to give board-like or strand-like woodbase materials. Examples of such lignocellulose-containing moldings or woodbase materials are medium density fiber boards (MDF), wood particle materials, such as particle boards and oriented strand boards (OSB), plywood, such as veneered plywood, and glued wood.
Binders used are as a rule formaldehyde-containing binders, for example urea-formaldehyde resins or melamine-containing urea-formaldehyde resins. The resins are prepared by polycondensation of formaldehyde with urea and/or melamine. The use of such formaldehyde resins can lead to the presence of free formaldehyde in the finished woodbase material. By hydrolysis of the polycondensates, additional formaldehyde may be liberated. The free formaldehyde present in the woodbase material and the formaldehyde liberated by hydrolysis during the life of the woodbase material can be released to the environment.
Above certain limits, formaldehyde can cause allergies and irritation of the skin, respiratory tract and eyes in humans. The reduction of the formaldehyde emission in components, especially in the interior sector, is therefore an important challenge.
The prior art discloses the following measures for reducing or suppressing the formaldehyde emission from woodbase materials:
However, such measures are still not completely satisfactory. The preparation of the aminoplast glues with little formaldehyde or the addition of formaldehyde scavengers to the aminoplast glue leads to the glue curing more slowly, which increases the residence times in the hot press and thus adversely affects the cost-efficiency of the production of the woodbase material.
WO 2010/031718 A1 (BASF SE) describes a multilayer lignocellulose-containing molding comprising a middle layer and a covering layer in which the binder for the middle layer is formaldehyde resin and/or organic isocyanate and the binder for the covering layer comprises a (co)polymer of ethylenically unsaturated carboxylic acids with further ethylenically unsaturated monomers and, under certain preconditions, a formaldehyde scavenger. WO 2010/031718 A1 does not disclose an organic isocyanate as a component of the binder for the covering layer.
The multilayer moldings described in the prior art still leave room for improvements with respect to mechanical strengths (for example transverse tensile strength, peeling strength of the layers according to the corresponding test standard mentioned in the examples) and also moisture resistance (for example 24 hour swelling or water absorption according to the test standard or test prescription mentioned in the examples).
The object of the present invention is accordingly to overcome the disadvantages described in the prior art. In particular, it was intended to provide multilayer lignocellulose-containing moldings whose formaldehyde emission was to be reduced or virtually absent, and the multilayer lignocellulose-containing moldings being intended to have good mechanical properties.
The object was achieved by a multilayer lignocellulose-containing molding comprising
The term lignocellulose is known to the person skilled in the art. Important examples of lignocellulose are wood, bark, cork, bagasse, straw, flax, bamboo, alfa grass, rice shells, sisal fibers and coir fibers. The material can be present in the form of granules, strands, shavings, fibers or flour. Very suitable examples of lignocellulose-containing particles are wood parts, such as wood layers, wood strips, wood chips or wood fibers, it being possible for the wood fibers to originate, if appropriate, also from wood fiber-containing plants, such as flax, hemp, sunflowers, Jerusalem artichoke or rape.
Wood particles, flax particles, in particular wood fibers or wood chips, and flax fibers or flax chips, the latter generally being referred to as flax shives, are preferred as lignocellulose-containing particles.
The abovementioned lignocellulose in the abovementioned forms can naturally also be used in mixtures, for example mixtures of wood fibers with flax fibers or wood chips with flax shives.
The binder (a) comprises a formaldehyde resin, preferably aminoplast resin (a1) and/or an organic isocyanate having at least two isocyanate groups (a2).
If the binder (a) comprises an aminoplast resin, the binder (a) as a rule also comprises the substances known to the person skilled in the art, generally used for aminoplasts and usually designated as curing agents, such as ammonium-sulfate or ammonium-nitrate or inorganic or organic acids, for example sulfuric acid, formic acid, or acid-generating substances, such as aluminum chloride, aluminum sulfate, in each case in the customary, small amounts, for example in the range from 0.1% by weight to 6% by weight, based on the total amount of aminoplast resin in the binder (a).
A formaldehyde resin is understood here as meaning polycondensates of compounds having at least one carbamido group (the carbamido group also called a carboxamido group) optionally partly substituted by organic radicals and an aldehyde, preferably form aldehyde; these resins are also called aminoplast resins. Formaldehyde resins are furthermore understood herein as meaning phenol-formaldehyde resins (PF resins).
All formaldehyde resins known to the person skilled in the art, preferably those known for the production of woodbase materials, can be used as suitable formaldehyde resin.
Such resins and their preparation are described, for example, in Ullmanns Enzyklopädie der technischen Chemie, 4th, revised and extended edition, Verlag Chemie, 1973, pages 403 to 424 “Aminoplaste” and Ullmann's Encyclopedia of Industrial Chemistry, vol. A2, VCH Verlagsgesellschaft, 1985, pages 115 to 141 “Amino Resins” and in M. Dunky, P. Niemz, Holzwerkstoffe and Leime, Springer 2002, pages 251 to 259 (UF resins) and pages 303 to 313 (MUF and UF with small amount of melamine, the latter also known as melamine-fortified UF resins (UFm)). Phenol-formaldehyde resins (PF resins) are also suitable formaldehyde resins.
Preferred formaldehyde resins are polycondensates of compounds having at least one carbamido group, including those partly substituted by organic radicals, and formaldehyde.
Particularly preferred formaldehyde resins are urea-formaldehyde resins (UF resins), melamine-formaldehyde resins (MF resins) or melamine-containing urea-formaldehyde resins (MUF resins and UFm resins) and melamine-urea-phenol-formaldehyde resins (MUPF resins).
Very particularly preferred formaldehyde resins are urea-formaldehyde resins (UF resins) and melamine-formaldehyde resins (MUF resins and UFm resins), for example Kaurit® or Kauramin® glue types from BASF SE.
In addition to the described conventional formaldehyde resins having a very high molar formaldehyde:amino group ratio, it is also possible to use formaldehyde resins having a lower molar formaldehyde:amino group ratio.
Such suitable formaldehyde resins, in particular aminoplast resins, are polycondensates of compounds having at least one amino group, including those partly substituted by organic radicals, and aldehyde, in which the molar ratio of aldehyde to amino group optionally partly substituted by organic radicals is in the range from 0.3 to 1.0, preferably from 0.3 to 0.6, particularly preferably from 0.4 to 0.5.
Further suitable formaldehyde resins of this type, in particular aminoplast resins, are polycondensates of compounds having at least one amino group-NH2 and formaldehyde, in which the molar ratio of formaldehyde to —NH2 group is in the range from 0.3 to 1.0, preferably from 0.3 to 0.6, particularly preferably from 0.4 to 0.5.
Further suitable formaldehyde resins of this type, in particular aminoplast resins, are urea-formaldehyde resins (UF resins) or melamine-containing urea-formaldehyde resins (MUF resins and UFm resins), in which the molar ratio of formaldehyde to —NH2 group is in the range from 0.3 to 1.0, preferably from 0.3 to 0.6, particularly preferably from 0.4 to 0.5.
Further suitable formaldehyde resins of this type, in particular aminoplast resins, are urea-formaldehyde resins (UF resins), in which the molar ratio of formaldehyde to —NH2 group is in the range from 0.3 to 1.0, preferably from 0.3 to 0.6, particularly preferably from 0.4 to 0.5.
The abovementioned conventional formaldehyde resins, in particular aminoplast resins, having a lower formaldehyde content are usually used in liquid form, in general suspended in a liquid suspending medium, preferably in aqueous suspension, but can also be used as a solid.
The solids content of the formaldehyde resin suspensions, preferably aqueous suspension, is usually from 25 to 90% by weight, preferably from 50 to 70% by weight.
The solids content of an aminoplast resin as a representative of formaldehyde resins in aqueous suspension can be determined, for example, according to Günter Zeppenfeld, Dirk Grunwald, Klebstoffe in der Holz- und Möbelindustrie, 2nd edition, DRW—Verlag, page 268. For determining the solids content of aminoplast glues, 1 g of aminoplast glue is accurately weighed into a weighing dish, finely distributed on the bottom and dried for 2 hours at 120° C. in a drying oven. After thermostating at room temperature in a desiccator, the residue is weighed and is calculated as a percentage of the weight taken.
The aminoplast resins are prepared by known processes (cf. abovementioned Ullmann literature “Aminoplaste” and “Amino Resins”, and abovementioned literature Dunky et al.) by reacting compounds containing carbamido groups, preferably urea and/or melamine, with the aldehydes, preferably formaldehyde, in the desired molar carbamido group:aldehyde ratios, preferably in water as a solvent.
The desired molar ratio of aldehyde, preferably formaldehyde, to amino group optionally partly substituted by organic radicals can also be established by adding monomers carrying —NH2 groups to prepared, preferably commercial, aminoplast resins having a relatively high formaldehyde content. Monomers carrying NH2 groups are preferably urea and melamine, particularly preferably urea.
An optional component of the binder (a) (hereinafter referred to as (a2)) and a mandatory component of binder (b) (hereinafter referred to as (II)) is an organic isocyanate having at least two isocyanate groups.
All organic isocyanates known to the person skilled in the art, preferably those known for the production of woodbase materials or polyurethanes, can be used as suitable organic isocyanate (a2) and/or (II). Such organic isocyanates and their preparation and use are described, for example in Becker/Braun, Kunststoff Handbuch, 3rd revised edition, volume 7 “Polyurethane”, Hanser 1993, pages 17 to 21, pages 76 to 88 and pages 665 to 671.
Preferred organic isocyanates (a2) and/or (II) are oligomeric isocyanates having 2 to 10, preferably 2 to 8, monomer units and on average at least one isocyanate group per monomer unit.
A particularly preferred organic isocyanate (a2) and/or (II) is the oligomeric organic isocyanate PMDI (“Polymeric Methylenediphenylene diisocyanate”) which is obtainable by condensation of formaldehyde with aniline and phosgenation of the isomers and oligomers formed in the condensation (cf. for example Becker/Braun, Kunststoff Handbuch, 3rd revised edition, volume 7 “Polyurethane”, Hanser 1993, page 18, last paragraph to page 19, second paragraph and page 76, fifth paragraph).
The organic isocyanate (a2) and/or (II) can also be present in aqueous-emulsifiable form, as obtainable for example by (i) adding emulsifiers, for example polyethylene glycols, glue, polyvinylpyrrolidone, polyacrylamides, or (ii) by modifying with monofunctional polyethylene oxide derivatives or by adding phosphoric or sulfonic acids.
In the context of the present invention, very suitable PMDI products (a2) and/or (II) are the products of the LUPRANAT® series of BASF SE, in particular LUPRANAT® M 20 FB of BASF Polyurethanes GmbH or the water-emulsifiable form of the ELASTAN® series of BASF Polyurethanes GmbH.
It is also possible to use mixtures of the organic isocyanates described, the mixing ratio not being critical on the basis of current knowledge.
The binder (a) may comprise the components (a1) and (a2) in all mixing ratios or alone.
In a preferred embodiment, the binder (a) comprises only the component (a1), preferably an aminoplast resin, particularly preferably a UF resin and/or MUF resin and/or UFm resin.
In a further preferred embodiment, the binder (a) comprises only the component (a2), preferably PMDI.
In a further preferred embodiment, the binder (a) comprises the component (a1), preferably an aminoplast, particularly preferably a UF resin and/or UFm resin and/or MUF resin, in the range from 70 to 99.9% by weight, and the component (a2), preferably PMDI, in the range from 0.1 to 30% by weight, based in each case on the sum of (a1) and (a2) of the pure undiluted substances.
In a very particularly preferred embodiment, the binder (a) comprises a UF resin in the range from 70 to 99.9% by weight and PMDI in the range from 0.1 to 30% by weight, based in each case on the sum of (a1) and (a2) of the pure, undiluted substances.
The binders (a1) and (a2) can be used in an already mixed form, but it is also possible to bring the binders (a1) and (a2), as a rule initially unmixed, into contact with the lignocellulose-containing particles, usually in separate steps.
The total amount of the binder (a1), preferably of the UF resin, as pure, undiluted substance, based on the dry mass of the lignocellulose-containing particles, preferably wood particles, is in the range from 3 to 50% by weight, preferably from 5 to 15% by weight, particularly preferably from 6 to 12% by weight.
The total amount of the binder (a2), preferably of the PMDI, as pure, undiluted substance, based on the dry mass of the lignocellulose-containing particles, preferably wood particles, is in the range from 0.5 to 30% by weight, preferably from 1 to 10% by weight, particularly preferably from 2 to 6% by weight.
Where the binder (a) is composed of (a1) and (a2), the total amount of the binder (a), as pure undiluted substance, based on the dry mass of the lignocellulose-containing particles, preferably wood particles, is in the range from 0.5 to 30% by weight, preferably from 1 to 15% by weight, particularly preferably from 2 to 12% by weight.
The binder (b) comprises:
An aqueous component (I) comprising
The polymer A is composed of the following monomers:
The preparation of polymers A is familiar to the person skilled in the art and is effected in particular by free radical solution polymerization, for example in water or in an organic solvent (cf. for example A. Echte, Handbuch der Technischen Polymerchemie, chapter 6, VCH, Weinheim, 1993 or B. Vollmert, Grundriss der Makromolekularen Chemie, volume 1, E. Vollmert Verlag, Karlsruhe, 1988).
Suitable monomers A1 are in particular α,β-monoethylenically unsaturated mono- and dicarboxylic acids having three to six carbon atoms, the possible anhydrides thereof and the water-soluble salts thereof, in particular the alkali metal salts thereof, such as, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, tetrahydrophthalic acid, or the anhydrides thereof, such as, for example, maleic anhydride, and the sodium or potassium salts of the above-mentioned acids. Acrylic acid, methacrylic acid and/or maleic anhydride are particularly preferred, acrylic acid and the binary combinations of acrylic acid and maleic anhydride or acrylic acid and maleic acid being especially preferred.
Suitable monomer(s) A2 are ethylenically unsaturated compounds which can be subjected to free radical copolymerization in a simple manner with monomer(s) A1, for example ethylene, C3-C24-α-olefins, such as propene, 1-hexene, 1-octene, 1-decene; vinylaromatic monomers, such as styrene, α-methylstyrene, o-chlorostyrene, or vinyltoluenes; vinyl halides, such as vinyl chloride or vinylidene chloride; esters of vinyl alcohol and monocarboxylic acids having 1 to 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate; esters of α,β-mono-ethylenically unsaturated mono- and dicarboxylic acids, preferably having 3 to 6 carbon atoms, such as, in particular, acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, with alkanols having in general 1 to 12, preferably 1 to 8 and in particular 1 to 4 carbon atoms, such as, in particular, methyl, ethyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and 2-ethylhexyl acrylate and methacrylate, dimethyl or di-n-butyl fumarate and maleate; nitriles of α,β-mono-ethylenically unsaturated carboxylic acids, such as acrylonitrile, methacrylonitrile, fumaronitrile, maleonitrile, and conjugated C4-8-dienes, such as 1,3-butadiene (butadiene) and isoprene. Said monomers form as a rule the main monomers which, based on the total amount of monomers A2, together account for a proportion of ≧50% by weight, preferably ≧80% by weight and particularly preferably ≧90% by weight or even the total amount of the monomers A2. As a rule, these monomers have only moderate to low solubility in water under standard conditions of temperature and pressure (20° C., 1 atm (absolute)).
Further monomers A2, which however have a high water solubility under the abovementioned conditions, are those which comprise either at least one sulfo group and/or the corresponding anion thereof or at least one amino, amido, ureido or N-heterocyclic group and/or the ammonium derivatives thereof which are protonated or alkylated on the nitrogen. Acrylamide and methacrylamide and furthermore vinyl-sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid and the water-soluble salts thereof and N-vinylpyrrolidone; 2-vinylpyridine, 4-vinylpyridine; 2-vinylimidazole; 2-(N,N-dimethylamino)ethyl acrylate, 2-(N,N-dimethylamino)ethyl methacrylate, 2-(N,N-diemethylamino)ethyl acrylate, 2-(N,N-diethylamino)ethyl methacrylate, 2-(N-tert.-butylamino)ethyl methacrylate, N-(3-N′,N′-dimethylamino-propyl)methacrylamide and 2-(1-imidazolin-2-onyl)ethyl methacrylate may be mentioned by way of example.
Usually, the abovementioned water-soluble monomers A2 are present only as modifying monomers in amounts ≦10% by weight, preferably ≦5% by weight and particularly preferably ≦3% by weight, based on the total amount of monomers A2.
Further monomers A2 which usually increase the internal strength of the films of a polymer matrix usually have at least one epoxy, hydroxyl, N-methylol or carbonyl group or at least two nonconjugated ethylenically unsaturated double bonds. Examples of these are monomers having two vinyl radicals, monomers having two vinylidene radicals and monomers having two alkenyl radicals. The diesters of dihydric alcohols with α,β-monoethylenically unsaturated monocarboxylic acids are particularly advantageous, among which acrylic and methacrylic acid are preferred. Examples of such monomers having two noncojugated ethylenically unsaturated double bonds are alkylene glycol diacrylates and dimethacrylates, such as ethylene glycol diacrylate, 1,2-propylene glycol diacrylate, 1,3-propylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylates and ethylene glycol dimethacrylate, 1,2-propylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, and divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, methylenebisacrylamide, cyclopentadienyl acrylate, triallyl cyanurate or triallyl isocyanurate. Also of particular importance in this context are C1-C8-hydroxyalkyl esters of methacrylic acid and of acrylic acid, such as n-hydroxyethyl, n-hydroxypropyl or n-hydroxybutyl acrylate and methacrylate, and compounds such as diacetoneacrylamide and acetylacetoxyethyl acrylate or methacrylate.
Frequently, the abovementioned crosslinking monomers A2 are used in amounts of ≦10% by weight, but preferably in amounts of ≦5% by weight, based in each case on the total amount of monomers A2. Particularly preferably, however, no such crosslinking monomers A2 at all are used for the preparation of the polymer A.
According to the invention, the proportion of monomers A2 which is incorporated in the form of polymerized units in the polymer A is advantageously ≦10% by weight or ≦5% by weight.
Particularly advantageously, the polymer A comprises no monomers A2 at all incorporated in the form of polymerized units.
Preferred polymers A are obtainable by free radical solution polymerization of only monomers A1, particularly preferably from 65 to 100% by weight, very particularly preferably from 70 to 90% by weight, of acrylic acid with particularly preferably from 0 to 35% by weight, very particularly preferably from 10 to 30% by weight, of maleic acid or maleic anhydride.
Advantageously, polymer A has a weight average molecular weight Mw in the range from 1000 g/mol to 500 000 g/mol, preferably from 10 000 g/mol to 300 000 g/mol, particularly preferably from 30 000 g/mol to 120 000 g/mol.
Establishing the weight average molecular weight Mw in the preparation of polymer A is familiar to the person skilled in the art and is advantageously effected by free radical aqueous solution polymerization in the presence of free radical chain-transfer compounds, the so-called free radical chain regulators. The determination of the weight average molecular weight Mw is also familiar to the person skilled in the art and is effected, for example, by means of gel permeation chromatography.
Suitable commercial products for polymers A are, for example, the Sokalan® products of BASF SE, which are based, for example, on acrylic acid and/or maleic acid. Further suitable polymers are described in WO 99/02591 A.
The component (I) optionally comprises a low molecular weight crosslinking agent (ii) having at least two functional groups which are selected from the group consisting of hydroxyl, carboxyl and derivatives thereof, primary, secondary and tertiary amine, epoxy, aldehyde.
Suitable crosslinking agents of this type are those having a (weight-average) molecular weight in the range from 30 to 10 000 g/mol. The following may be mentioned by way of example: alkanolamines, such as triethanolamine; carboxylic acids, such as citric acid, tartaric acid, butanetetracarboxylic acid; alcohols, such as glucose, sucrose or other sugars, glycerol, glycol, sorbitol, trimethylolpropane; epoxides, such as bisphenol-A or bisphenol-F and also resins based thereon and further polyalkylene oxide glycidyl ethers or trimethylolpropane triglycidyl ether. In a preferred embodiment of the invention, the molecular weight of the low molecular weight crosslinker (ii) used is in the range from 30 to 4000 g/mol and more preferably in the range from 30 to 500 g/mol.
Polymer M is composed of the following monomers:
Polymer M is obtainable by free radical emulsion polymerization of the corresponding monomers M1 and/or M2 in an aqueous medium. Polymer M may be present in a single-phase form or multiphase form, and can have a core/shell morphology.
The procedure for free radical emulsion polymerizations of ethylenically unsaturated monomers in an aqueous medium has been described before many times and is therefore sufficiently well known to the person skilled in the art (cf. for example: Emulsion Polymerisation in Encyclopedia of Polymer Science and Engineering, vol. 8, page 659 et seq. (1987); D. C. Blackley, in High Polymer Latices, vol. 1, page 35 et seq. (1966); H. Warson, The Applications of Synthetic Resin Emulsions, chapter 5, page 246 et seq. (1972); D. Diederich, Chemie in unserer Zeit 24, pages 135 to 142 (1990); Emulsion Polymerisation, Interscience Publishers, New York (1965); DE-A 40 03 422 and Dispersionen synthe-tischer Hochpolymerer, F. Hölscher, Springer-Verlag, Berlin (1969)).
The free radical aqueous emulsion polymerization reactions are usually effected in such a way that the ethylenically unsaturated monomers are dispersed with a concomitant use of dispersants in an aqueous medium in the form of monomer droplets and polymerized by means of a free radical polymerization initiator.
Suitable monomer(s) M1 are in particular glycidyl acrylate and/or glycidyl methacrylate and hydroxyalkyl acrylates and methacrylates having C2- to C10-hydroxyalkyl groups, in particular C2- to C4-hydroxyalkyl groups and preferably C2- and C3-hydroxyalkyl groups, for example 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate and/or 4-hydroxybutyl methacrylate. One or more, preferably one or two, of the following monomers M1 are particularly advantageously used: 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl acrylate, glycidyl methacrylate.
According to the invention, it is possible, optionally, initially to take a portion or the total amount of monomers M1 in the polymerization vessel. However, it is also possible to meter in the total amount or any remaining amount of monomers M1 during the polymerization reaction. The total amount or any remaining amount of monomers M1 can be metered into the polymerization vessel batchwise in one or more portions or continuously at constant or varying flow rates. Particularly advantageously, the metering of the monomers M1 is effected during the polymerization reaction continuously at constant flow rates, in particular as a constituent of an aqueous monomer emulsion.
Suitable monomer(s) M2 are in particular ethylenically unsaturated compounds which can undergo free radical copolymerization in a simple manner with monomer(s) M1, for example ethylene, vinylaromatic monomers, such as styrene, α-methyl styrene, o-chlorostyrene or vinyltoluenes; vinyl halides, such as vinyl chloride or vinylidine chloride; esters of vinyl alcohol and monocarboxylic acids having 1 to 18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl-n-butyrate, vinyl laurate and vinyl stearate; esters of α,β-monoethylenically unsaturated mono- and dicarboxylic acids having preferably 3 to 6 carbon atoms, such as, in particular, acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, with alkanols having in general 1 to 12, preferably 1 to 8 and in particular 1 to 4 carbon atoms, such as, in particular, methyl, ethyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and 2-ethylhexyl acrylate and methacrylate, dimethyl or di-n-butyl fumarate and maleate; nitriles of α,β-monoethylenically unsaturated carboxylic acids, such as acrylonitrile, methacrylonitrile, fumaronitrile, maleonitrile, and conjugated C4-8-dienes, such as 1,3-butadiene (butadiene) and isoprene. Said monomers form as a rule the main monomers which, based on the total amount of monomers M2, together account for a proportion of ≧50% by weight, preferably ≧80% by weight and in particular ≧90% by weight. As a rule, these monomers have only moderate to low solubility in water under standard conditions of temperature and pressure (20° C., 1 atm (absolute)).
Monomers M2 which have a high water solubility under the abovementioned conditions are those which comprise either at least one acid group and/or the corresponding anion thereof or at least one amino, amido, ureido or N-heterocyclic group and/or the ammonium derivatives thereof which are protonated or alkylated on the nitrogen. α,β-Monoethylenically unsaturated mono- and dicarboxylic acids having 3 to 6 carbon atoms and the amides thereof, such as, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide and methacrylamide, and furthermore vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid and the water-soluble salts thereof and N-vinylpyrrolidone, 2-vinylpyridine, 4-vinylpyridine, 2-vinylimidazole, 2-(N,N-dimethylamino)ethyl acrylate, 2-(N,N-dimethylamino)ethyl methacrylate, 2-(N,N-diethylamino)ethyl acrylate, 2-(N,N-diethyl-amino)ethyl methacrylate, 2-(N-tert.-butylamino)ethyl methacrylate, N-(3-N′,N′-dimethylaminopropyl)methacrylamide, 2-(1-imidazolin-2-onyl)ethyl methacrylate and ureido methacrylate may be mentioned by way of example. Usually, the abovementioned water-soluble monomers M2 are present only as modifying monomers in amounts of ≦10% by weight, preferably ≦5% by weight and particularly preferably ≦≦3% by weight, based on the total amount of monomers M2.
Monomers M2, which usually increase the internal strength of the films of a polymer matrix, usually have at least one N-methylol or carbonyl group or at least two nonconjugated ethylenically unsaturated double bonds. Examples of these are monomers having two vinyl radicals, monomers having two vinylidene radicals and monomers having two alkenyl radicals. The diesters of dihydric alcohols with α,β-monoethylenically unsaturated monocarboxylic acids are particularly advantageous, among which acrylic and methacrylic acid are preferred. Examples of such monomers having two nonconjugated ethylenically unsaturated double bonds are alkylene glycol diacrylates and dimethacrylates, such as ethylene glycol diacrylate, 1,2-propylene glycol diacrylate, 1,3-propylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylates and ethylene glycol dimethacrylate, 1,2-propylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, and divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate, methylenebisacrylamide, cyclopentadienyl acrylate, triallyl cyanurate or triallyl isocyanurate. Also of importance in this context are compounds such as diacetoneacrylamide and acetylacetoxyethyl acrylate or methacrylate. Frequently, the abovementioned crosslinking monomers M2 are used in amounts of 10% by weight, preferably in amounts of ≦5% by weight and particularly preferably in amounts of ≦3% by weight, based in each case on the total amount of monomers A2. Frequently, however, no such crosslinking monomers M2 at all are used.
According to the invention, it is possible, optionally, initially to take a portion or the total amount of monomers M2 in the polymerization vessel. However, it is also possible to meter in the total amount or any remaining amount of monomers M2 during the polymerization reaction. The total amount or any remaining amount of monomers M2 can be metered into the polymerization vessel batchwise in one or more portions or continuously at constant or varying flow rates. Particularly advantageously, the metering of the monomers M2 during the polymerization reaction is effected continuously at constant flow rates, in particular as a constituent of an aqueous monomer emulsion.
For the preparation of the aqueous dispersion of the component (II), frequently dispersants are concomitantly used which keep both the monomer droplets and the polymer particles obtained by the free radical polymerization dispersed in the aqueous phase and thus ensure the stability of the aqueous polymer composition produced. Both the protective colloids usually used for carrying out free radical aqueous emulsion polymerizations and emulsifiers are suitable as such.
Suitable protective colloids are, for example, polyvinyl alcohols, cellulose derivatives or copolymers comprising vinylpyrrolidone or acrylic acid, for example those defined herein as component I(i). A detailed description of further suitable protective colloids is to be found in Houben-Weyl, Methoden der organischen Chemie, volume XIV/1, Makromolekulare Stoffe, pages 411 to 420, Georg-Thieme-Verlag, Stuttgart, 1961.
Of course, mixtures of emulsifiers and/or protective colloids can also be used. Frequently, exclusively emulsifiers whose relative molecular weights in contrast to the protective colloids are usually below 1000 are used as dispersants. They may be anionic, cationic or nonionic. When mixtures of surface-active substances are used, the individual components must of course be compatible with one another, which in case of doubt can be checked by means of a few preliminary experiments. In general, anionic emulsifiers are compatible with one another and with nonionic emulsifiers. The same also applies to cationic emulsifiers, while anionic and cationic emulsifiers are generally not compatible with one another.
Customary emulsifiers are, for example, ethoxylated mono-, di- and trialkylphenoles (degree of EO: 3 to 50, alkyl radical: C4 to C12), ethoxylated fatty alcohols (degree of EO: 3 to 50; alkyl radical: C8 to CM) and alkali metal and ammonium salts of alkylsulfates (alkyl radical: C8 to C12), of sulfuric monoesters of ethoxylated alkanols (degree of EO: 3 to 30, alkyl radical: C12 to C18) and of ethoxylated alkylphenoles (degree of EO: 3 to 50, alkyl radical: C4 to C12), of alkanesulfonic acids (alkyl radical: C12 to C18) and of alkylarylsulfonic acids (alkyl radical: C9 to C18). Further suitable emulsifiers are to be found in Houben-Weyl, Methoden der organischen Chemie, volume XIV/1, Makromolekulare Stoffe, pages 192 to 208, Georg-Thieme-Verlag, Stuttgart, 1961.
Nonionic and/or anionic emulsifiers are preferably used for the process according to the invention.
As a rule, the amount of dispersant, in particular emulsifiers, used is from 0.1 to 5% by weight, preferably from 1 to 3% by weight, based in each case on the total amount of the monomer mixture M. In the event that protective colloids are used as sole dispersing auxiliaries, the amount used will be distinctly higher; the amount used is typically from 5% to 40% by weight of dispersing auxiliary, preferably from 10% to 30% by weight, all based on the total weight of the monomer mixture M.
According to the invention, it is possible, optionally, initially to take a portion or the total amount of dispersant in the polymerization vessel. However, it is also possible to meter in the total amount or any remaining amount of dispersant during the polymerization reaction. The total amount or any remaining amount of dispersant can be metered into the polymerization vessel batchwise in one or more portions or continuously at constant or varying flow rates. Particularly advantageously, the metering of the dispersants during the polymerization reaction is effected continuously at constant flow rates, in particular as a constituent of an aqueous monomer emulsion.
Preferred polymers M comprise a) from 0.01 to 50% by weight of at least one ethylenically unsaturated monomer which comprises at least one epoxide group and/or at least one hydroxyalkyl group (monomer(s) M1) and b) from 50 to 99.99% by weight of at least one further ethylenically unsaturated monomer which differs from the monomers M1 (monomer(s) M2).
Particularly preferred polymers M of this type are obtainable by free radical solution polymerization of from 10 to 30% by weight, preferably from 15 to 22% by weight, of esters of acrylic acid and/or methacrylic acid with C1-8-alcohols—preferably methanol, n-butanol, 2-ethylhexanol—with from 40 to 70% by weight, preferably from 55 to 65% by weight, of styrene and of from 5 to 50% by weight, preferably from 20 to 30% by weight, of 2-hydroxyethyl acrylate and/or 2-hydroxyethyl methacrylate and/or glycidyl acrylate and/or glycidyl methacrylate, the sum of the components being 100% by weight.
Further preferred polymers M comprise no monomer(s) M1 and are obtainable by free radical solution polymerization of from 80 to 99% by weight, preferably from 85 to 95% by weight, of esters of acrylic acid and/or methacrylic acid with C1-8-alcohols—preferably methanol, n-butanol, 2-ethylhexanol—with from 0 to 5% by weight, preferably from 1 to 3% by weight, of ureido methacrylate and of from 0.5 to 5% by weight, preferably from 1 to 4% by weight, of α,β-monoethylenically unsaturated mono- and dicarboxylic acids having 3 to 6 carbon atoms—preferably acrylic acid, methacrylic acid—and/or amides of these acids, the sum of the components being 100% by weight.
Further preferred polymers M are obtainable by using dispersing auxiliaries based on poly(acrylic acid)s as described in EP 1240205 A or DE19991049592 A.
Such polymers preferably have a core/shell morphology (isotropic distribution of the phases, for example in the form of onion skins) or a Janus morphology (anisotropic distribution of the phases).
By targeted variation of type and amount of monomers M1 and M2, it is possible for the person skilled in the art, according to the invention, to prepare aqueous polymer compositions whose polymers M have a glass transition temperature Tg or a melting point in the range from −60 to 270° C.
Advantageously, the glass transition temperature Tg of the polymer M is in the range from 10° C. to 120° C. and preferably in the range from 30° C. to 90° C.
The glass transition temperature Tg, is understood as meaning the limit of the glass transition temperature toward which the glass transition temperature tends with increasing molecular weight, according to G. Kanig (Kolloid-Zeitschrift & Zeitschrift für Polymere, vol. 190, page. 1, equation 1). The glass transition temperature or the melting point is determined by the DSC method (Differential Scanning calorimetry, 20 K/min, midpoint measurement, DIN 53765).
The Tg values for the homopolymers of most monomers are known and are listed, for example, in Ullmann's Encyclopedia of Industrial Chemistry, part 5, vol. A21, page 169, VCH Weinheim, 1992; further sources of glass transition temperatures of homopolymers are, for example, J. Brandrup, E. H. Immergut, Polymer Handbook, 1st Ed., J. Wiley, New York 1966, 2nd Ed. J. Wiley, New York 1975, and 3rd Ed, J. Wiley, New York 1989).
The components (I) and (III) according to the invention usually have polymer solids contents (total amount of polymer A or total amount of polymer M) of ≧10 and ≦70% by weight, frequently ≧20 and ≦65% by weight and often ≧40 and ≦60% by weight, based on the respective aqueous component (I) or (II).
The number average particle diameter (cumulant z average) of the polymer M, determined via quasielastic light scattering (ISO standard 13321), in the aqueous component (III) is as a rule from 10 to 2000 nm, frequently from 20 to 1000 nm and often from 50 to 700 nm or from 80 to 400 nm.
The components of the binder (b), preferably the components (I) and (III), can be used ready-mixed, but it is also possible for the components of the binder (b) to be in a generally initially unmixed state when they are brought into contact with the lignocellulose-containing particles, typically in separate steps.
The total amount of the components (I) and (III) of the binder (b) as a pure, undiluted substance, based on the dry mass of the lignocellulose-containing particles, preferably wood particles, is in the range from 0.5% to 50% by weight, preferably in the range from 0.75% to 12% by weight and more preferably in the range from 1% to 6% by weight.
The total amount of the component (I) of the binder (b) as a pure, undiluted substance, based on the dry mass of the lignocellulose-containing particles, preferably wood particles, is in the range from 0.5% to 30% by weight, preferably in the range from 1% to 10% by weight and more preferably in the range from 1.5% to 6% by weight.
The total amount of the component (III) of the binder (b) as a pure, undiluted substance, based on the dry mass of the lignocellulose-containing particles, preferably wood particles, is in the range from 0.5 to 30% by weight, preferably in the range from 0.75% to 10% by weight and more preferably in the range from 1 to 6% by weight.
The weight ratio of component (I):component (III) of the binder (b) as a pure, undiluted substance is in the range from 10:1 to 1:10 preferably 5:1 to 1:5 and more preferably 3:1 to 1:3.
The pH of the binder (b) is in the range from 0 to 5, preferably in the range from 2 to 4. The desired pH of the binder B arises as a rule by the combination of the components (I) and (III) and, optionally, component (IV) and/or formaldehyde scavenger.
The pH of the binder (b) at the place of action can, however, be adjusted to the desired value in the range from 0 to 5, preferably in the range from 2 to 4, in a customary manner by addition of inorganic or organic acids and/or salts thereof, for example mineral acids, such as sulfuric acid, hydrochloric acid, phosphorus-containing acids such as phosphoric acid, phosphorous acid or hypophosphorous acid and salts thereof, for example sodium phosphate, sodium phosphite, sodium hypophosphite; organic sulfonic acids, such as methanesulfonic acid, carboxylic acids, such as formic acid or acetic acid, or sodium formate, sodium acetate, sodium citrate, or inorganic or organic bases, for example sodium hydroxide (aqueous or as such), calcium oxide or calcium carbonate (in each case aqueous or as such) or ammonia, aqueous or as such.
In general, the ready-mixed binder (b) having the abovementioned pH ranges can be used. The desired pH—as described above—can, however, also be adjusted by applying the individual components of the binder (b) and the acids or bases described above separately to the lignocellulose-containing substrate. Through the choice of the pH of the components of the binder (b) and of the added acids or bases, the person skilled in the art can combine them so that the desired pH is established on the lignocellulose-containing substrate.
The term additive as component (IV) is to be understood as meaning all additives known to the person skilled in the art, for example waxes, paraffin emulsion, flame-retardant additives, wetting agents, salts, but also inorganic or organic acids and bases, for example mineral acids, such as sulfuric acid or nitric acid, phosphorus-containing acids such as phosphoric acid, phosphorous acid or hypophosphorous acid; organic sulfonic acids, such as methanesulfonic acid, carboxylic acids, such as formic acid or acetic acid, or inorganic or organic bases, for example sodium hydroxide (aqueous or as such), calcium oxide or calcium carbonate (in each case aqueous or as such) or ammonia, aqueous or as such. These additives can be added in an amount of from 0 to 20% by weight, preferably from 0 to 5% by weight, in particular from 0 to 2% by weight, based on the dry mass of the lignocellulose-containing particles, for example absolutely dry wood.
The lignocellulose-containing particles, preferably wood particles, particularly preferably wood chips or fibers, are coated with glue as a rule by bringing into contact with the binder (a) or (b). So-called glue application methods of this type are known for the production of conventional woodbase materials with customary aminoplast resins and are described, for example, in “Taschenbuch der Spanplatten Technik”, H.-J. Deppe, K. Ernst, 4th edition, 2000, DRW—Verlag Weinbrenner GmbH & Co., Leinfelden-Echter-dingen, chapter 3.3.
The binder (a) or (b) can be brought into contact with the lignocellulose-containing particles, preferably wood particles, particularly wood chips or fibers, in various ways, preferably by spraying (a) or (b) onto the lignocellulose-containing particles.
In the glue application, the binder (a) or (b) is usually used in such amounts as described above.
As far as the binder (b) is concerned, it is preferable for the component (II) not to be premixed with the further components (I) and/or (III) and/or (IV) when it is brought into contact with the lignocellulose-containing particles. The component (II) can be brought into contact with the lignocellulose-containing particles at a time before or after the other aforementioned components.
The binder (b) optionally comprises a formaldehyde scavenger.
The binder (b) preferably comprises a formaldehyde scavenger if the binder (a) comprises a formaldehyde resin as described above.
Formaldehyde scavenger refers to chemical substances which as a rule have a free electron pair which reacts chemically with the formaldehyde, i.e. chemically binds the formaldehyde, as a rule virtually irreversibly. Such free electron pairs are present, for example, on the following functional groups of organic or inorganic compounds: primary, secondary and tertiary amino groups, hydroxyl group, sulfite group, amides, imides.
Examples of suitable formaldehyde scavengers are: ammonia, urea, melamine, organic C1-C10-amines, polymers which carry at least one amino group, such as polyamines, polyimines, polyureas, polylysines, polyvinylamine, polyethylenimine. Urea is a particularly preferred formaldehyde scavenger.
The amount of the formaldehyde scavengers in the binder (b) is in the range from 0.1 to 10% by weight, preferably from 0.5 to 7% by weight, based on the dry mass of the lignocellulose-containing particles, for example absolutely dry wood, and pure, undiluted formaldehyde scavenger.
The multilayer lignocellulose-containing moldings may have a regular or irregular three-dimensional shape. The following are examples of suitable desired shapes: all regular moldings, such as spheres, cylinders, cuboids, boards; all irregular shapes, such as irregular cavities, ornaments.
Preferred desired shapes are sheet-like, the form of a board being particularly preferred.
Further preferred multilayer lignocellulose-containing moldings comprise more than 70% by weight of lignocellulose-containing particles, preferably wood fibers, wood chips, flax fibers or flax shives.
The average density of the multilayer lignocellulose-containing moldings is usually in the range from 300 kg/m3 to 950 kg/m3, preferably from 450 kg/m3 to 850 kg/m3.
The multilayer lignocellulose-containing moldings according to the invention have a middle layer or a plurality of middle layers A) comprising lignocellulose-containing particles and a binder (a) and a covering layer or two covering layers (B) comprising lignocellulose-containing particles and a binder (b).
In the context of the invention, middle layer or middle layers is or are all layers which are not the outer layers.
The outer layer or the outer layers of the multilayer lignocellulose-containing moldings according to the invention are also referred to here as covering layer or covering layers.
Preferred multilayer lignocellulose-containing moldings according to the invention are sheet-like, preferably in the form of a board, comprising, for example, flax particles and/or wood particles, particularly preferably wood chips or wood fibers, as lignocellulose-containing particles, and have three layers; a middle layer A) and one covering layer B) each on the top and bottom thereof.
For the production of the multilayer lignocellulose-containing moldings, for example of the abovementioned, three-layer lignocellulose-containing moldings, the following binders are preferably used for the respective layers:
In a very suitable embodiment, the binder (b) comprises a component (III) but no low molecular weight crosslinker (ii), as will now be described by way of example under variants 1 and 2.
For the middle layer A) or the middle layers A), the binder (a) comprises only the component (a1), preferably an aminoplast resin, particularly preferably a UF resin and/or MUF resin.
For a covering layer B) or the two covering layers B), the binder (b) is used; for example, the binder (b) comprises an aqueous solution of a polymer A according to the invention, obtainable by free radical solution polymerization of 70% by weight of acrylic acid and 30% by weight of maleic anhydride in water. The component (I) comprises no further crosslinking component. The component (III) of the binder (b) is an aqueous dispersion of a polymer M according to the invention, obtainable by free radical emulsion polymerization of from 50 to 65% by weight of styrene and from 5 to 15% by weight of methyl methacrylate, from 5 to 15% by weight of n-butyl acrylate, from 10 to 30% by weight of hydroxyethyl acrylate and from 2 to 20% by weight of glycidyl methacrylate in water, the sum of the monomers being 100% by weight.
The binder (b) furthermore comprises the component (II) in the amounts defined above and a formaldehyde scavenger as defined above, in the amounts as defined there.
For the middle layer A) or the middle layers A), the binder (a) comprises the component (a1), preferably an aminoplast, particularly preferably a UF resin and/or MUF resin, and the component (a2), preferably PMDI, in the amounts defined above for the combination (a1) and (a2).
For a covering layer B) or the two covering layers B), the binder (b) is used; for example, the binder (b) comprises an aqueous solution of a polymer A according to the invention, obtainable by free radical solution polymerization of 70% by weight of acrylic acid and 30% by weight of maleic anhydride in water. The component (I) comprises no further crosslinking component. The component (III) of the binder (b) is an aqueous dispersion of a polymer M according to the invention, obtainable by free radical emulsion polymerization of from 50 to 65% by weight of styrene and from 5 to 15% by weight of methyl methacrylate, from 5 to 15% by weight of n-butyl acrylate, from 10 to 30% by weight of hydroxyethyl acrylate and from 2 to 20% by weight of glycidyl methacrylate in water, the sum of the monomers being 100% by weight.
The binder (b) furthermore comprises the component (II) in the amounts defined above and a formaldehyde scavenger as defined above, in the amounts as defined there.
In a further very suitable embodiment, the binder (b) comprises a low molecular weight crosslinker (ii) and no component (III), as will now be described by way of example under variants 3 to 5.
For the middle layer A) or the middle layers A), the binder (a) comprises only the component (a1), preferably an aminoplast resin, particularly preferably a UF resin and/or MUF resin.
For a covering layer B) or the two covering layers B), the binder (b) is used; for example, the binder (b) comprises an aqueous solution of a polymer A according to the invention, obtainable by free radical solution polymerization of 70% by weight of acrylic acid and 30% by weight of maleic anhydride in water. The component (I) additionally comprises a crosslinker component (ii), preferably having more than two functional groups per crosslinker molecule, particularly preferably triethanolamine.
The binder (b) further comprises the component (II) in the amounts defined above and a formaldehyde scavenger as defined above, in the amounts as defined there.
For the middle layer A) or the middle layers A), the binder (a) comprises only the component (a2), preferably PMDI.
For a covering layer B) or the two covering layers B), the binder (b) is used; for example, the binder (b) comprises an aqueous solution of a polymer A according to the invention, obtainable by free radical solution polymerization of 70% by weight of acrylic acid and 30% by weight of maleic anhydride in water. The component (I) additionally comprises a crosslinker component (ii), preferably having more than two functional groups per crosslinker molecule, particularly preferably triethanolamine.
The binder (b) further comprises the component (II) in the above-defined amounts but no formaldehyde scavenger.
For the middle layer A) or the middle layers A), the binder (a) comprises the components (a1) and (a2), preferably PMDI.
For a covering layer B) or the two covering layers B), the binder (b) is used, but without the component (III); for example, the binder (b) comprises an aqueous solution of a polymer A according to the invention, obtainable by free radical solution polymerization of 70% by weight of acrylic acid and 30% by weight of maleic anhydride in water. The component (I) additionally comprises a crosslinker component (ii), preferably having more than two functional groups per crosslinker molecule, particularly preferably triethanolamine.
The binder (b) further comprises a component (II) in the above-defined amounts and a formaldehyde scavenger as defined above, in the amounts as defined there.
In a further highly suitable embodiment, the binder (b) comprises both a low molecular weight crosslinker (ii) and a component (III), as described hereinbelow by way of example under variant 6.
For the middle layer A) or the middle layers A), the binder (a) comprises the component (a1), preferably an amino resin, particularly preferably a UF resin and/or MUF resin, and/or the component (a2), preferably PMDI in the amounts defined above for the combination (a1) and (a2).
For a covering layer B) or the two covering layers B), the binder (b) is used; for example, the binder (b) comprises an aqueous solution of a polymer A according to the invention, obtainable by free radical solution polymerization of 70% by weight of acrylic acid and 30% by weight of maleic anhydride in water. The component (I) additionally comprises a crosslinker component (ii), preferably having more than two functional groups per crosslinker molecule, particularly preferably triethanolamine. The component (III) of the binder (b) is an aqueous dispersion of a polymer M according to the invention, obtainable by free radical emulsion polymerization in water of 50% to 65% by weight of styrene and 5% to 15% by weight of methyl methacrylate, 5% to 15% by weight of n-butyl acrylate, 10% to 30% by weight of hydroxyethyl acrylate and 2% to 20% by weight of glycidyl methacrylate, the sum total of the monomers being 100% by weight.
The binder (b) further comprises the component (II) in the above-defined amounts and a formaldehyde scavenger as defined above in the amounts as defined there.
The thickness of the multilayer lignocellulose-containing moldings, preferably the board-like moldings, according to the invention varies with the field of application and is generally in the range from 0.5 to 300 mm; preference is given to relatively thin board-like moldings having a thickness in the range from 4 to 100 mm and in particular in the range from 6 to 40 mm.
The thickness ratios of the layers of the multilayer lignocellulose-containing moldings according to the invention, preferably of the board-like moldings, are variable. Usually, the outer layers A), also referred to as covering layers, by themselves or in total, are thinner than the layer or layers of the middle layer(s) B).
The mass of the individual covering layer is usually in the range from 5 to 30% by weight, preferably from 10 to 25% by weight, of the total mass of the multilayer lignocellulose-containing molding according to the invention.
In the preferred multilayer lignocellulose-containing molding according to the invention, preferably the board-like molding, the thickness of the middle layer(s) B), based on the total thickness of the multilayer lignocellulose-containing molding according to the invention, preferably the board-like molding, is in the range from 20% to 99%, preferably from 50% to 99%, particularly preferably from 60% to 99%.
The multilayer lignocellulose-containing moldings according to the invention, preferably those in which the lignocellulose-containing particles are wood particles and/or flax particles, particularly preferably wood chips or wood fibers, or flax chips or flax shives, are produced in the customary manner, as described in “Taschenbuch der Spanplatten Technik” H.-J. Deppe, K. Ernst, 4th edition, 2000, DRW—Verlag Weinbrenner GmbH & Co., Leinfelden-Echterdingen, chapter 3.5.
Usually, first lignocellulose-containing particles, for the middle layer(s) A) and the covering layer(s) B), for example wood or flax, preferably wood, for example in the form of fibers, chips, veneers or strands, as described above, are brought into contact (also referred to as “glue-coated”) with the respective binder (a) (for the middle layer(s) A)) or (b) (for the covering layer(s) B)).
Thereafter, the lignocellulose-containing particles, for example wood or flax, preferably wood, for example in the form of fibers, chips, veneers or strands, glue-coated in this manner are placed in layers one on top of the other according to the desired sequence of the multilayer lignocellulose-containing molding to be produced and are pressed at elevated temperature by a customary method to give multilayer lignocellulose-containing moldings, preferably those in which the lignocellulose-containing particles are wood, for example in the form of fibers, chips, veneers or strands.
For this purpose, a fiber/chip mat is usually produced by sprinkling the lignocellulose-containing particles glue-coated in this manner, for example wood or flax—preferably wood, particularly preferably wood in the form of chips or fibers—onto a substrate and said mat is usually pressed at temperatures of from 80° C. to 250° C. and at pressures of from 5 to 50 bar to give multilayer lignocellulose-containing moldings according to the invention (cf. for example: “Taschenbuch der Spanplatten Technik” H.-J. Deppe, K. Ernst, 4th edition, 2000, DRW—Verlag Weinbrenner GmbH & Co., Leinfelden-Echterdingen, pages 232-254. “MDF—Mitteldichte Faserplatten” H.-J. Deppe, K. Ernst, 1996, DRW—Verlag Weinbrenner GmbH & Co., Leinfelden-Echterdingen, pages 93-104).
The pressing times needed for board production are typically specified in “seconds per mm of board thickness”; or s/mm (often also referred to as pressing time factor). Multilayer lignocellulose-containing moldings according to the invention generally require pressing time factors of the kind known for the quick formaldehyde resins; a Siempelkamp laboratory press (dimensions 520 mm×520 mm) generally requires pressing time factors of 8 to 10 s/mm for moldings according to the invention, and also for boards produced using aminoplast-containing binders only; moldings produced with formaldehyde-free binders, for example products of the Acrodur® product range from BASF SE, require pressing time factors of more than 25 s/mm.
Particularly preferred multilayer lignocellulose-containing moldings according to the invention are all those which are produced from wood strips, for example veneer sheets or plywood sheets, or multilayer lignocellulose-containing moldings produced from wood chips, for example particle boards or OSB boards, and multilayer wood fiber materials, such as LDF, MDF and HDF boards.
Woodbase materials comprising formaldehyde-free binders are advantageously produced by the process according to the invention. Multilayer OSB boards, wood fiber boards and particle boards are preferred.
The present invention furthermore relates to the use of the multilayer lignocellulose-containing moldings according to the invention, preferably the multilayer wood-containing moldings according to the invention, for the production of pieces of furniture, of packaging materials, in house building, in drywall construction or in interior finishing, for example as laminate, insulating material, wall or ceiling element, or in motor vehicles.
The multilayer lignocellulose-containing moldings according to the invention show a greatly reduced emission of formaldehyde or virtually no emission of formaldehyde and are obtainable using very short pressing times.
The multilayer lignocellulose-containing moldings according to the invention moreover show increased peel strength for the covering layers, good transverse tensile strength and good moisture resistance.
Amounts reported in % OD are weight percent based on the net mass of dry wood; OD stands for oven dry.
Formaldehyde emissions were determined by the following test methods for woodbase materials (see also Bundesgesetzblatt 10/91, p. 488/489):
The mechanical properties of woodbase materials were evaluated by determining the following parameters:
Water absorption was determined similarly to DIN EN 317 except that it is not the thickness of the test specimen which is determined before and after 24 hour water immersion but its mass, by weighing. The water absorption WA of each test specimen as a percentage of the initial mass must be computed by the following formula: WA=100×(m2−m1)/m1.
In this formula:
Water absorption is reported to one decimal place.
Wood moisture was determined to DIN 52183.
Production of multilayer lignocellulose-containing moldings,
in particular the production of 3-layer laboratory chipboard
A certain amount of sprucewood chips (conditioned at 20° C. and 65% relative humidity) plus additives was resinated with the stated amounts of binder and binder components in a Lödige mixer. Resination was done in two steps when isocyanates were used as binders, otherwise unless otherwise stated in one step. The resinated chips were measured for chip moisture content. The chips for covering and middle layers were treated separately from each other.
Thereafter, the chips were manually formed into mats: first a covering layer, then the middle layer and finally the second covering layer in a mass ratio of 1 part of covering layer chips, then 4 parts of middle layer chips and again 1 part of covering layer chips. The mat was hot-pressed at 210° C. using the molding pressure profile reported in the examples.
The three-layer lignocellulose-containing moldings produced in the tests were tested for their properties using the methods indicated above.
Binders according to the present invention were used in the examples which follow, specifically:
A commercially available aqueous solution of a polymer B52, obtainable by free radical solution polymerization of 70% by weight of acrylic acid and 30% by weight of maleic anhydride in water. The weight average molecular weight Mw was 80 000 g/mol. To 100 parts of this polymer were added, as crosslinker component, 30 analogous parts of triethanolamine, based on the solids content of the polymer solution. The solids content of the admixture was 50% by weight.
For clarity, each individual component of polymer mixture B is listed separately in the tables of the examples.
The middle layer binders used were KAURIT® resins from BASF SE (KL=Kaurit® resin).
Several laboratory chipboard panels having dimensions of 56.5 cm*44.0 cm*16.0 mm were produced using different binder compositions. The target envelope density for the panels was 680 kg/m3.
Molding pressure profile: 65 s at 4 bar, 65 s at 2 bar, 90 s at 1 bar
Table 1A reports the binder batches for the various board panels. Amount recitations without explicit units are by mass. Columns headed “MS” identify the binder for the middle layer, columns headed “DS” identify the binder for the covering layers.
Batches 1 and 2 constitute conventional comparative boards corresponding to the prior art as described in WO/2010/031718. The resin used in the middle layer was BASF product KL337.
Batch 3 is an inventive chipboard where the covering layer comprises PMDI.
The inventive chipboard 3 clearly evinces, compared with 1 and 2, reduced 24 h swelling and water absorption and also increased transverse tensile strength and peel strength.
Several laboratory chipboard panels having dimensions of 56.5 cm*44.0 cm* 16.0 mm were produced using different binder compositions. The target envelope density for the panels was 680 kg/m3.
Molding pressure profile: 65 s at 4 bar, 65 s at 2 bar, 90 s at 1 bar
Table 2A reports the binder batches for the various board panels. Amount recitations without explicit units are by mass. Columns headed “MS” identify the binder for the middle layer, columns headed “DS” identify the binder for the covering layers.
Batches 1 and 2 constitute conventional comparative boards corresponding to the prior art as described in WO/2010/031718. The resin used in the middle layer was BASF product KL340.
Batch 3 is an inventive chipboard where the covering layer comprises PMDI.
The inventive chipboard 3 clearly evinces, compared with 1 and 2, reduced 24 h swelling and water absorption and also increased transverse tensile strength and peel strength.
Several laboratory chipboard panels having dimensions of 56.5 cm*44.0 cm* 16.0 mm were produced using different binder compositions. The target envelope density for the panels was 680 kg/m3.
Molding pressure profile: 65 s at 4 bar, 65 s at 2 bar, 90 s at 1 bar
Table 3A reports the binder batches for the various board panels. Amount recitations without explicit units are by mass. Columns headed “MS” identify the binder for the middle layer, columns headed “DS” identify the binder for the covering layers.
Batch 1 constitutes conventional comparative boards corresponding to the prior art as described in WO/2010/031718.
Batches 2 and 3 are an inventive chipboard where the covering layer comprises PMDI. The inventive chipboards 2 and 3 clearly evince, compared with 1, reduced 24 h swelling and water absorption and also increased transverse tensile strength and peel strength.
Several laboratory chipboard panels having dimensions of 56.5 cm*44.0 cm* 16.0 mm were produced using different binder compositions. The target envelope density for the panels was 670 kg/m3.
Molding pressure profile: 65 s at 4 bar, 65 s at 2 bar, 90 s at 1 bar
Table 4A reports the binder batches for the various board panels. Amount recitations without explicit units are by mass. Columns headed “MS” identify the binder for the middle layer, columns headed “DS” identify the binder for the covering layers.
The mass ratio of the covering layers to the middle layer was DS:MS:DS=1:4:1. The layers were formed by hand and then hot-pressed at 210° C. using the following molding pressure profile: 50 s at 4 bar, 50 s at 2 bar, 40 s at 1 bar.
Batch 4 constitutes an inventive comparative board similar to boards 2 and 3 of example 1. In batches 1 to 3 the covering layer additionally incorporates methanesulfonic acid.
Particularly batches 2 and 3 are observed to give increased transverse tensile strength, reduced swelling values and slightly reduced formaldehyde emissions. In all three cases (1-3) peel strength is improved over the board without added acid (4).
Several laboratory chipboard panels having dimensions of 56.5 cm*44.0 cm* 16.0 mm were produced using different binder compositions. The target envelope density for the panels was 670 kg/m3.
Molding pressure profile: 65 s at 4 bar, 65 s at 2 bar, 90 s at 1 bar
Table 5A reports the binder batches for the various board panels. Amount recitations without explicit units are by mass. Columns headed “MS” identify the binder for the middle layer, columns headed “DS” identify the binder for the covering layers.
The chipboard panels thus produced were coated with decor paper and tested for the quality of the coating. The results are shown in table 5B.
Columns at left (designations 1-A, 2-A and 3-A): melamine short cycle coating The boards were coated with already pre-impregnated papers from DKB Dekor Kunststoffe GmbH (Erndtebrück-Schameder). The sequence of the layers was as follows: backer→chipboard→decor foil→overlay
Molding conditions: 180° C./2.5 N/mm2/40 sec.
Columns at right (designations 1-B, 2-B and 3-B): lamination with furniture foil (adhered with white glue)
Unimpregnated decor paper (light granite decor) having a raw weight of 200 g/m2 had a liquor batch based on Kaurit®-Tranksystem impregnating system (see hereinbelow) applied to it by means of a “0/0” rod blade (resin application 48%). The papers thus impregnated were dried at 120° C. for 175 seconds, the residual moisture content of the furniture foil thus produced was found to be 6.7%. The chipboard to be tested was coated with the same furniture foil on both sides.
Molding conditions: 95° C./0.5 N/mm2/4 min.
100 parts by weight of KTS820 (=Kaurit®-Tränksystem 820) impregnating system 60 parts by weight of water
2 parts by weight of a 60% solution of para-toluenesulfonic acid
The liquor resulting therefrom has a 100° C. gel time of about 200 sec.
Resin add-on and residual moisture content of the furniture foil were determined by differential weighing (unimpregnated paper/impregnated paper after above drying/impregnated paper after additional drying at 180° C./2 min).
The saw cut involved sawing 3 times in each case with the circular saw into the coated board to a depth of about 5 cm. The drill test was done by drilling 3 times through each board with a 6 mm drill from above and below. In the milling test a 6 mm countersinking head was used to cut into the upper side of the previously produced drill-hole. The crosshatch test involves using a carpet knife to make cuts in the form of a square grid (4×4, separation about 1 cm) through the coating down to the wood. A strip of adhesive tape (Tesa/Scotch) is then stuck onto the grid, pushed down by hand and torn off again abruptly. To make the test tougher, a knife can then be used to mechanically work over the crossing points of the cuts.
Experimental series A corresponds to a chipboard as described in WO/2010/031718. Experimental series B corresponds to an inventive chipboard with PMDI in binder (b). Experimental series C corresponds to a chipboard fully bonded with aminoplast resin. While no qualitative differences are observable between the furniture foil-laminated test specimens (designations 1-B, 2-B and 3-B), the short cycle-coated test specimens (designations 1-A, 2-A and 3-A) produce distinct differences in some instances: improved quality is discernible for inventive test specimen 2-A compared with the 1-A test specimens without PMDI in the covering layer bonded with a formaldehyde-free binder; this quality is equivalent to that of conventionally aminoplast-bonded woodbase materials (cf. 3-A).
Results Table with Mechanicals and FA Values
Several laboratory chipboard panels having dimensions of 51.0 cm*51.0 cm*16.0 mm were produced using different binder compositions. The target envelope density for the panels was 650 kg/m3. The boards were produced to using a pressing time factor of 14 s/mm.
Table 6A reports the binder batches for the various board panels.
Columns headed “MS” identify the binder for the middle layer, columns headed “DS” identify the binder for the covering layers.
The mass ratio of the covering layers to the middle layer was DS:MS:DS=1:4:1. The layers were formed by hand and then hot-pressed at 210° C. using the following molding pressure profile: 50 s at 4 bar, 50 s at 2 bar, 40 s at 1 bar.
Batch 1 constitutes an inventive comparative board similar to boards 2 and 3 of example 1. In batches 2 to 5, the amount of urea in the covering layer as formaldehyde scavenger is additionally increased compared with batch 1.
The mechanical properties of all the boards are comparable. Only formaldehyde emission decreases with increasing amount of urea in the covering layers. The formaldehyde emissions in batch 4 are almost 50% reduced compared with the emissions of batch 1 (F****).
Several laboratory chipboard panels having dimensions of 51.0 cm*51.0 cm*16.0 mm were produced using different binder compositions. The target envelope density for the panels was 650 kg/m′. The boards were produced to using a pressing time factor of 14 s/mm.
Table 7A reports the binder batches for the various board panels. Columns headed “MS” identify the binder for the middle layer, columns headed “DS” identify the binder for the covering layers.
The mass ratio of the covering layers to the middle layer was DS:MS:DS=1:4:1. The layers were formed by hand and then hot-pressed at 210° C. using the following molding pressure profile: 50 s at 4 bar, 50 s at 2 bar, 40 s at 1 bar.
Batch 1 constitutes an inventive comparative board similar to boards 2 and 3 of example 1. In batches 2 to 4, the covering layer has an increased amount of isocyanate in the binder and at the same time a reduced amount of polymer B52.
The mechanical properties of all the boards are comparable. Only water stability increases with increasing amount of isocyanate in the covering layers: the swell values decrease from batch 1 to batch 4.
The codes used in the tables for the substances have the following meanings:
KL 337 or KL 340, or KL 347: each Kaurit®-Leim resin from BASF SE, in each case an aqueous solution or dispersion of a UF resin; dry resin content 65% to 70% by weight.
KL 465: Kaurit®-Leim from BASF SE, aqueous solution or dispersion of a UFm resin; dry resin content 65% to 70% by weight.
Hydrowax® 560 or Hydrowax® Q: each a hydrophobicizing agent from Sasol based on paraffin, each aqueous emulsions; solids content 60% and 50%, respectively. Lupranat® M20 FB: PMDI from BASF Polyurethanes GmbH
| Number | Date | Country | |
|---|---|---|---|
| 61381447 | Sep 2010 | US |
