POE-free adhesion promoters for sustainable timber construction

Abstract

The invention relates to adhesive systems for lignocellulosic composite materials comprising a) a primer composition, b) an NCO-containing adhesive composition.

Description

[0001] 202400200 1

[0002] POE-free adhesion promoters for sustainable timber construction

[0003] Field of the invention

[0004] The invention relates to adhesive systems for lignocellulosic materials consisting of isocyanate (NCO)- containing adhesive formulations and an adhesion promoter based on polyglycerols or polyglycerol partial esters for the pretreatment of the substrate that improves the bonding of difficult-to-bond substrates.

[0005] Prior art

[0006] Concrete is the most important building material of our times. However, concrete production is an emissions-intensive industrial process that results in significant greenhouse gas emissions. Structural glued laminated timber construction is one solution for avoiding greenhouse gas emissions in the construction sector. Products in structural glued laminated timber construction such as OSB (oriented strand board), CLT (cross-laminated timber), GLT (glulam, glue-laminated timber) and LVL (laminated veneer lumber) consist of wood materials (for example wood lamellas, veneers, shavings, fibres, chemically-modified or infiltrated wood) and adhesives. Examples of adhesives are pMDI (polymeric / oligomeric diphenylmethane diisocyanate), PF (phenol / formaldehyde) and MF (melamine / formaldehyde). Adhesives approved in the EU for load-bearing applications belong to the families of emulsion polymer isocyanate (EPI) adhesives (DIN EN16254 (2016)), phenoplastic and aminoplastic resins (DIN EN 301 (2018)) or polyurethane (PUR) adhesives (DIN EN 15425 (2017)) and must meet high strength requirements. A test to examine the effect of moisture and heat on the strength of the adhesive join is the longitudinal tensile shear test on beech wood test specimens in the wet state after boiling for 6 h, as described in DIN EN 302-1 A4 (2017). Further important tests to examine the effect of moisture are delamination tests, which are described for example in DIN EN 14080 (2013) Annex C and EN 302-2 (2017). Of the adhesive types mentioned, those having isocyanate functionality are particularly noteworthy, since these do not result in formaldehyde emissions during processing and cure at room temperature within practicable times.

[0007] At present, structural glued laminated timber construction mainly involves working with products based on softwood (usually spruce, occasionally fir, pine, larch or Douglas fir; other types of softwood are possible). This is also reflected in the current European standards for CLT (DIN EN 16351 :2021) and GLT (DIN EN 14080:2013), which only apply to components made of softwoods and poplar. However, the increasingly rapidly changing climatic conditions and the threat from pests such as bark beetles have made a transition to the processing of other lignocellulosic materials necessary. For this reason, hardwoods, particularly beech and oak wood, are increasingly being used in structural glued laminated timber construction. For example the documents Z-9.1-679 (beech), Z-9.1-821 (oak) and EAD 130320-00-0304 (various hardwoods) for GLT and EAD 130010-01-0304 for GLT made of LVL lamellas have been created for this purpose. These documents for hardwood products likewise refer to the already mentioned delamination tests. 202400200 2

[0008] However, the problem arises that the currently available products for structural glued laminated timber construction based on hardwood that meet the abovementioned technical specifications (EAD) and general technical approvals (Z) are largely or exclusively bonded with aminoplasts and phenoplasts. Standard 1 -component polyurethane adhesives (1 K-PUR) belong to the family of “NCO-containing adhesive compositions” and, although having the advantages of not resulting in formaldehyde emissions during processing, not requiring any separate handling of resin-curing agents, and of curing at room temperature within practicable times, on hardwoods they often do not meet the strength requirements specified in the standards, particularly with respect to the delamination test.

[0009] This problem with 1 K-PUR adhesive formulations is known. One solution in principle is the use of adhesive systems consisting of a primer (adhesion promoter) and the 1 K-PUR adhesive formulation. For this, the primer is applied to the wood first and only after a primer-specific exposure time is the adhesive formulation applied. The increasing importance of primers is demonstrated inter alia by the fact that primers were included under the name adhesion promoters in the draft standard with publication date 2022-01-07 for the new DIN EN 15425. However, unsolved challenges still arise in the case of the already known adhesive systems with 1 K-PUR and primers for structural glued laminated timber construction.

[0010] For example, US5543487 describes a primer based on hydroxymethylated resorcinol (HMR) that improves bonding with epoxy adhesives and, as shown by a review study by Richter et al. (International Journal of Adhesion and Adhesives 113 (2022) 103070), also improves bonding using 1 K-PUR. However, it is necessary for the HMR primer to be freshly produced and to react for a defined time prior to application, which must be neither undershot nor overshot. Moreover, it is based on the toxicologically harmful chemicals formaldehyde and resorcinol, the processing of which requires a high level of safety. It is for these reasons that adhesive systems consisting of 1 K-PUR and the HMR primer have not been adopted in industry.

[0011] A structurally similar primer is disclosed in US5888655. This primer is a carbamate-functional novolac resin for aminoplast adhesives, the use of which is however restricted to aminoplast adhesives. US 5888655 does not include examples for use on wood, or in adhesive systems with 1 K-PUR.

[0012] US2009191354 uses primer formulations consisting of a strong inorganic base and polyethylenimine (PEI) that have a pH of at least 11 .5, and discloses the use thereof for the bonding of hardwoods from various eucalyptus types. A tensile strength test that departs from the above-described standards is described, which is used to demonstrate that the PEI primer increases the tensile strength of a 1 K-PUR adhesive on various eucalyptus types. However, no information is given as to whether this applies in the wet state too. Results of delamination tests, as required in the standards cited above, are not described. A further problem is that the strongly basic nature of the solutions makes the primer unattractive for industrial use. The bases containing NaOH and KOH that are described therein can cause blindness if coming into contact with the eyes and should therefore be sprayed only with special safety precautions. 202400200 3

[0013] Moreover, alkali metal hydroxides have a corrosive effect on metal. A further problem is the long exposure time of the PEI primer of 1-4 hours, which would slow down throughput in industrial production.

[0014] WO03093385 discloses an adhesive system consisting of a 1 K-PUR and a primer, wherein a solution of polyvinyl alcohol, salts of dodecylbenzenesulfonic acid, copolymers based on ethene and vinyl acetate, or a urea solution are possible as primer. The described adhesive system does however require that the wood first be planed and then additionally treated with sandpaper so that the requirements of the standard in the wet state laid down in standard ASTM D2559 are met. However, sandpaper is not normally used in an industrial-scale adhesion process, which is why the described primers are unsuitable for industrial production. Also, the delamination test from ASTM D2559 is passed only with softwood of longleaf pine. Douglas fir exhibits excessive delamination. Other wood types, particularly hardwoods, have not been tested, but it must be assumed that many hardwoods cannot be bonded with these adhesive systems, since their standards-compliant 1 K-PUR bonding is considered more difficult than the bonding of Douglas fir, which was not possible with the described primers.

[0015] WO2023069254 claims an adhesive system comprising a primer composition consisting of water, alkyl sulfosuccinate, a POE phenol derivative and a flame retardant. However, the positive effect of the primers is shown only on softwoods, in particular southern yellow pine. Also, the described primer comprises POE-octylphenol (CAS = 9002-93-1), which is not only very harmful to aquatic organisms, but also counts as a potential endocrine disruptor and should therefore be used only if absolutely necessary and with the use of special safety precautions.

[0016] EP2848638 describes adhesive systems containing 1 K-PUR and a primer composition, wherein the primer composition comprises polyalkylene glycols and / or mono- and / or diethers thereof having an OH value (OHV) of 30 mg KOH / g or less. The described primer composition may optionally also comprise a solvent and / or a surfactant. EP2848638 states that these adhesive systems are particularly suitable for woods with a high proportion of extractables, in particular the extractable arabinogalactan. The patent specifies as wood types containing a high proportion of arabinogalactan, almost exclusively softwoods (larch, hemlock, black spruce, Douglas fir, cedar, juniper). Sugar maple is mentioned as sole hardwood type having a high proportion of arabinogalactan. The efficacy of the adhesive system is demonstrated only on larch. There is no use of hardwood, for example beech, in the examples. The examples comprise exclusively delamination tests in accordance with EN 391 Method B. The standard has in the meantime been withdrawn, but the test is comparable to the currently valid delamination test from the successor standard DIN EN 14080 (2013) Method B.

[0017] According to DIN EN 14080 (2013), the maximum permissible delamination in a delamination test in accordance with Method B corresponds to 4%. Of the nine inventive example adhesive formulations shown in EP2848638, only four meet this requirement. Although this does show that some of the primers increase the water resistance of the adhesive join itself in the delamination test, no results are given on the effect of the primers on the shear strength of the bonded test specimens, for example in the longitudinal tensile shear test according to DIN EN 302-1 (2017) A1 or A4 or compressive shear test 202400200 4 according to DIN EN 14080 (2013) Annex D. However, proof of shear strength is essential for industrial use. The examples shown have a primer exposure time of 10 minutes to 24 hours. Short exposure times would be desirable for industrial use, since exposure times of several minutes require interim storage of the lignocellulosic materials (generally wood lamellas) to be bonded, which complicates the process and slows down production throughput.

[0018] EP2928977 is likewise dedicated to adhesive systems containing primers. Examples 1-4 show how the use of polysorbate 20 (Tween™ 20, polyoxyethylene (20) sorbitan monolaurate), polysorbate 81 (Tween™ 81 , polyoxyethylene (5) sorbitan monooleate) and Surfynol PSA-336 (formulation of ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol) with specific wood species in specific tests of adhesive join strength leads to improved results. Specifically, it is shown that pretreatment with a 5% polysorbate 20 primer solution can improve the bonding of Douglas fir, as measured by shear strength and wood tearout in the CSA 112.0 test. The same primer solution likewise slightly improves the delamination resistance of southern yellow pine from an average of 6% to 1-4.6% (depending on primer exposure time and amount of primer solution).

[0019] The addition of 1% Surfynol PSA-336 to the 5% polysorbate 20 primer solution made it possible to improve the delamination resistance on southern yellow pine from 4.6% to 1 .8%. A 1% PSA-336 solution without polysorbate 20 causes delamination of 4.3%. Polysorbate 81 has a similar effect to polysorbate 20 on southern yellow pine.

[0020] The primer solution comprising 5% polysorbate 20 and 1% PSA-336 also shows delamination of 5% on eucalyptus, 4% on ash, 8% on beech and 0% on birch. In example 5, a 0.5% polysorbate 20 primer solution showed delaminations of 14% on ash, 5% on beech and 0% on birch. On the basis of the results shown, both primer compositions would meet the requirements in the delamination test of Method B of DIN EN 14080 (2013) of max. 4% delamination solely for birch, but birch is not considered to be a good construction timber on account of its low load-bearing capacity and low durability.

[0021] The general technical approval Z-9.1-765 of 11 .8.2022 also describes combining the primer Loctite PR 3105 Purbond® (as described in EP2928977) with adhesives of the Loctite HB SX9 Purbond® line, which makes it possible to bond not only softwoods (spruces, firs, pines, Douglas fir) but also European beech in a standards-compliant manner. However, the cited adhesive system comprising HB SX9 Purbond® and Loctite PR 3105 Purbond® is unsuitable for use with larch. For the bonding of larch, the general technical approval specifies the primer PR 7010 based on the polyethers described in EP2848638.

[0022] Apart from beech, the technical approval does not mention any further hardwoods.

[0023] What the primers described in EP2848638 and EP2928977 have in common is that they are based on compounds containing polyoxoethylene (POE). In the respective compounds, the POE structural units bring about adequate water solubility and are accordingly critical for the useability of the described primers. However, POE-containing compounds also have some disadvantages: 202400200 5

[0024] - The preparation of compounds containing POE uses ethylene oxide. Ethylene oxide is highly volatile, corrosive, toxic, carcinogenic, mutagenic and can cause fertility impairment. Replacing ethylene oxide with non-hazardous substances in the industrial production of primers is desirable. POE structural units in commercially available structures are nowadays usually petrochemicalbased. The production of POE-containing compounds from petrochemical sources brings carbon into circulation that is then converted into CO2 by combustion or biological degradation, which escapes into the atmosphere and intensifies the greenhouse effect. It is therefore generally desirable to replace petrochemical-based structural units with biobased structural units in which the carbon present therein has been removed from the atmosphere in the form of CO2 by plants. POE and POE-containing compounds are currently a focus of intense discussion in the academic literature as allergy triggers. The use of compounds without allergy-triggering properties is generally preferred. This is particularly true of uses in which the compounds are sprayed, as is also the case for the application of primers.

[0025] Object

[0026] Despite some developments in the field, there still remains the unachieved object of providing a primer that permits the bonding of a wide range of woods. This should prime not just easy-to-bond softwoods, such as spruce, but also harder-to-bond softwoods such as Douglas fir, as well as difficult-to-bond hardwoods such as beech, such that they are able to undergo bonding with NCO-containing adhesive compositions (inter alia 1 K-PUR adhesives) into a material that, in the demanding DIN EN 14080 (2013) Method B delamination test, displays only little delamination and at the same time has good shear strength. In addition, the primers to be provided should contain no POE or POE derivatives. An additional object is to provide a method for bonding with the adhesive systems of the invention and the uses thereof.

[0027] Achievement

[0028] The object was achieved by providing an adhesive system for the production of lignocellulosic composite materials, comprising a) a primer composition b) a moisture-curing NCO-containing adhesive composition wherein the primer composition comprises:

[0029] 1-100% by weight of polyglycerol partial esters and / or polyglycerols, preferably 1-30% by weight

[0030] 0-15% by weight of surfactants

[0031] 0-99% by weight of solvents, preferably 55-95% by weight. 202400200 6

[0032] The object was achieved by providing a primer composition based on polyglycerol partial esters and / or polyglycerols. Polyglycerol partial esters and / or polyglycerols mean in this context not just polyglycerol partial esters alone or polyglycerols alone, but also mixtures of polyglycerol partial esters with polyglycerols.

[0033] It was found that in particular primer compositions containing 1-100% by weight, more preferably 50- 100% by weight, of polyglycerol partial esters and / or polyglycerols is suitable as primer concentrate for the uses according to the invention in the adhesive system.

[0034] It was also found that in particular primer compositions containing 1-30% by weight of polyglycerol partial esters and / or polyglycerols are suitable as applicable primer solution for the uses according to the invention in the adhesive system. These (diluted) primer compositions are optionally marketed with surfactants (0-15% by weight), and 55-95% by weight of solvents as saleable product, or are prepared by the user prior to application by addition of solvents.

[0035] It was surprisingly found that the use of a 10% by weight aqueous primer solution comprising polyglyceryl-4 caprate significantly improved by 61-78% the delamination resistance of NCO-containing adhesive compositions on Douglas fir and beech. The longitudinal tensile shear strength and compressive shear strength of bonded wood test specimens are also significantly improved by the pretreatment with the primer of the invention compared to the noninventive primers. In addition to beech and Douglas fir, the primer is also suitable for the bonding of other difficult-to-bond hardwood species, softwoods and other lignocellulosic materials.

[0036] Very particular preference is therefore given to adhesive systems for the production of lignocellulosic composite materials comprising a) a primer composition b) a moisture-curing NCO-containing adhesive composition wherein the primer composition comprises:

[0037] 1-100% by weight of polyglyceryl-4 caprate, polyglyceryl-3 caprate, polyglycerol-4 or polyglycerol-3, preferably 1-30% by weight 0-15% by weight of surfactants and

[0038] 0-99% by weight of solvents, preferably 5-95% by weight.

[0039] The primer composition according to the invention comprising polyglycerol partial esters and / or polyglycerols is superior to many other primer compositions in that it does not contain POE. There is accordingly no need for toxic ethylene oxide to be used for their preparation and they do not possess the allergy-triggering potential of POE.

[0040] The abbreviation POE means “polyoxoethylene” and is used hereinbelow as a synonym both for pure polyalkylene glycols having a polyoxoethylene component, for example polyethylene glycol 200, and as a synonym for molecules containing a covalently attached POE unit. The general notation “POE (n) compound” refers to a derivative of a compound that has been reacted formally with n units of ethylene 202400200 7 oxide to form a POE-containing derivative. POE-containing derivatives are also referred to in the literature as “alkoxylated” or “ethoxylated” derivatives.

[0041] The primer compositions according to the invention comprise polyglycerol partial esters and / or polyglycerols and optionally additional surfactants. The polyglycerol partial esters and / or polyglycerols can potentially be classified as surfactants, but in the context of this invention are intended to describe a separate group, separate from other surfactants.

[0042] The polyglycerol partial esters and / or polyglycerols may be prepared petrochemically. They are however preferably prepared from renewable raw materials.

[0043] The preferred polyglycerol partial esters are preferably obtainable by esterification or transesterification of polyglycerols with at least one fatty acid, or with mixtures of at least one fatty acid and at least one mono-, di- or polyfunctional carboxylic acid (polycarboxylic acids) or acyl donors derived therefrom. Any acyl group donors may be used according to the invention. These are for example carboxylic esters or carboxylic acids themselves and mixtures thereof.

[0044] Particular preference is given to polyglycerol partial esters selected from the group of polyglycerol partial esters with monocarboxylic acids.

[0045] The term “polyglycerols” should be understood for the purposes of the present invention as meaning a polyglycerol mixture that may in particular comprise glycerol oligomers and glycerol. Any glycerol component should therefore also be taken into consideration when calculating amounts, masses and the like. Because of their polymeric nature, the polyglycerols constitute a mixture of various compounds. Polyglycerol may have ether linkages between two primary, one primary and one secondary, or else two secondary alcohol positions of the glycerol monomers. For this reason, the polyglycerol base skeleton does not normally consist exclusively of linearly linked glycerol units, but may also contain branches and rings. For details, see for example “Original synthesis of linear, branched and cyclic oligoglycerol standards”, Cassel et al., J. Org. Chem. 2001 , 875-896.

[0046] The same applies to the term “polyglycerol partial esters” in connection with the present invention. The polyglycerols present in the polyglycerol partial esters of the invention are covalently attached.

[0047] The polyglycerols of the invention and the polyglycerols present in the polyglycerol partial esters of the invention have an average degree of polymerization N of 1 .1 to 20, preferably 2.5 to 16 and very particularly preferably 2.6 to 12.

[0048] The polyglycerol partial esters or polyglycerols of the invention have a hydroxyl value of 10-1400 mg KOH / g.

[0049] In particular, the polyglycerol partial esters of the invention conform to the general structural formula (I): 202400200 8 wherein the repeat units may be arranged in any desired order, where k + I = 1 .1-20, preferably 2.5-16, more preferably 2.6-12, and

[0050] R1= each independently identical or different H, -C(=O)-R2, -C(=O)-R3or -R3radicals, where

[0051] R2= each independently identical or different alkyl radicals or alkenyl radicals having 1 to 21 carbon atoms or aryl radicals having 6-18 carbon atoms, preferably alkyl and alkenyl radicals having 5-17 carbon atoms, more preferably alkyl radicals having 5-15 carbon atoms, and

[0052] R3= each independently identical or different radicals composed of 1-18 bridging methylene units -CH2- and / or -CH(CH2OH)- units, where the methylene units can be part of a bridging dicarboxylic acid unit, wherein in structure (I) on average at least 4% of the radicals R1must be different from H and preferably at least one radical is -C(=O)-R2or -C(=O)-R3.

[0053] In the structural formulas shown for the described polymers, the indices indicate the amounts of the individual repeat units in the theoretical molecule, number-averaged across the polymer distribution. In the individual molecules actually present, the specified repeat units may be present within the polymer distribution in blocks, in random order or in another order. The following structures are an exception, which are titled “Example structures conforming to general structural formula (I)”.

[0054] Example structures for primers of the invention that conform to the general formula (I) are shown below:

[0055] 202400200 9

[0056] Example structures conforming to general structural formula (I)

[0057] Polyglycerol partial esters preferred according to the invention are obtainable by esterification or transesterification of mixtures of polyglycerols with at least one fatty acid, or with mixtures of at least one fatty acid and at least one mono-, di- or polyfunctional carboxylic acid (polycarboxylic acids) or acyl donors derived therefrom.

[0058] Any acyl group donors may be used according to the invention. These are for example carboxylic esters, carboxylic anhydrides or carboxylic acids themselves and mixtures thereof.

[0059] Suitable reaction conditions for the esterification or transesterification are temperatures of between 120°C and 260°C and atmospheric pressure or else reduced pressure in a range of between 20 mbar and 800 mbar, in particular between 50 and 500 mbar. The esterification or transesterification may be carried out in the presence of catalytic amounts of a base, in particular selected from metal hydroxides, metal oxides and metal carbonates such as NaOH, Ca(OH)2, KOH, Zn(OH)2, CaO, ZnO, Na2CO3, CaCOs or K2CO3, or catalytic amounts of an acid, in particular sulfuric acid, phosphoric acid, phosphinic acid, methanesulfonic acid, ethanesulfonic acid or para-toluenesulfonic acid. Corresponding processes can be found in standard chemistry textbooks such as Rompp.

[0060] Surfactants

[0061] The primers according to the invention may contain 0-15% by weight from the group of water-soluble surfactants, water-dispersible surfactants and mixtures thereof.

[0062] Preferred surfactants are organically modified siloxanes, acetylenediol derivatives, alkoxylated fatty alcohols, sulfosuccinates, alkyl polyglycosides and biosurfactants such as Rheance® One (from Evonik, Germany). 202400200 10

[0063] Moisture-curing NCO-containing adhesive composition

[0064] The NCO-containing adhesive formulations for the bonding of lignocellulosic materials in each case have an NCO content of 1-32% by weight, which was measured according to DIN EN ISO 11909 (2007).

[0065] The main component of the NCO-containing adhesive formulations is either polymeric methylene diphenyl diisocyanate (pMDI) or an isocyanate prepolymer prepared from at least one diisocyanate, for example one or more isomers of methylene diphenyl diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated methylene diphenyl diisocyanate and / or a higher isocyanate, for example pMDI or trimers, oligomers or homopolymers of the aforementioned diisocyanates and / or mixtures thereof comprising two or more of said isocyanates and at least one isocyanate-reactive substance used in a substoichiometric amount, usually an alcohol compound and / or amine compound, often in the form of polymers, i.e. polyols composed of different monomers.

[0066] Particularly preferred are moisture-curing NCO-containing adhesive compositions characterized in that they contains prepolymers formed by reaction of polyether polyols and aromatic isocyanates having two or more NCO functionalities and that they have an NCO content of 1-28% by weight, preferably of 1-20% by weight, more preferably of 10-20% by weight.

[0067] Likewise preferably, NCO-containing adhesive compositions are characterized in that they contain polymeric diphenylmethane diisocyanate (pMDI) as main component and have an NCO content of 28- 32% by weight.

[0068] Formulations and also production processes and in some cases subsequent mixtures of individual separately produced prepolymers are known to those skilled in the art, are well described, such as in WO 02 / 48232 or US 6133398 for example, and to a large extent form the basis of polyurethane-based adhesive chemistry.

[0069] In addition to the prepolymers and / or pMDI, the NCO-containing adhesive formulations may contain further additives or / and auxiliaries. By way of example, crosslinkers, fillers, catalysts, defoamers, stabilizers, acids, antioxidants, UV stabilizers, biocides and other ageing stabilizers, viscosity modifiers, plasticizers, dyes, solvents, dispersants, adhesion promoters, flame retardants, hydrolysis stabilizers, desiccants, activators and further auxiliaries and mixtures thereof may be present.

[0070] The crosslinkers are preferably selected from the group of oligomers or homopolymers of hexamethylene diisocyanate, one or more mixed isomers of methylene diphenyl diisocyanate, pentamethylene diisocyanate and isophorone diisocyanate and mixtures thereof.

[0071] Suitable fillers are metal oxides, for example titanium dioxide, aluminium oxide, zinc oxide, fumed silicon dioxide, surface-treated silicas, sheet silicates such as kaolin, mica, bentonite, or talc, and carbon black. Likewise suitable are biobased fillers such as cornflour, wheat flour and ground nutshells. Further 202400200 11 preferably, the fillers are selected from the group of CaCOs, reinforcing fibres, organic polymers, preferably lignin or cellulose, and mixtures thereof.

[0072] Suitable catalysts include tin(ll) salts of carboxylic acids, alkyltin(IV) carboxylates, tertiary amines, amino alcohols, alkali metal hydroxides and alkali metal alkoxides. Preferred catalysts of the NCO-containing adhesive formulations according to the invention are selected from the group of Polycat® DMDEE (dimorpholinodiethyl ether) Polycat® 557 (from Evonik, Germany), dialky Itin(IV) dicarboxylates, dialkyltin(IV) thiols, dialky Iti n(IV) thioglycolates and mixtures thereof. It is in addition possible to use a large number of other catalysts, for example those mentioned in EP 1425328.

[0073] Plasticizers, solvents and thinners suitable for the NCO-containing adhesive compositions are esters, for example castor oil, diesters of phthalic acid, aliphatic diacids, such as adipic acid, or triacids, for example citric acid, and further plasticizers, solvents and thinners known to those skilled in the art.

[0074] Suitable desiccants for preventing premature curing in the event of moisture ingress during storage and priming are for example molecular sieve powder, silanes, diethyl malonate and alkyl phenol acrylates.

[0075] Hydrolysis stabilizers are substances that are intended to reduce the hydrolysis of the fully cured adhesive join.

[0076] Suitable antioxidants and UV stabilizers are for example phenol derivatives, thioesters, phosphates or sterically inhibited amines marketed for this purpose.

[0077] Suitable adhesion promoters (not in the function as primer pretreatment) in the NCO-containing adhesive compositions are di- or trialkoxysilanes.

[0078] Suitable flame retardants are for example bromoalkyl or chloroalkyl phosphate esters, melamine, aluminium oxide hydrate, red phosphorus, ammonium polyphosphate, antimony trioxide.

[0079] Suitable defoamers, hydrolysis stabilizers, antioxidants and viscosity modifiers are known to those skilled in the art.

[0080] There are various NCO-containing adhesive systems that contain NCO-containing adhesive formulations. In addition to the adhesive formulations already mentioned, NCO-containing adhesive systems may also contain primers. These are used to treat the wood materials to be bonded prior to application of the adhesive composition, thereby achieving an improvement in adhesive strength, particularly in wet adhesive strength.

[0081] Solvents

[0082] Suitable solvents for the primer composition are DMSO, water, alcohols, glycols, levoglucosenone, other polar solvents and mixtures thereof. Preferred solvent for the primer composition is water. 202400200 12

[0083] The adhesive systems according to the invention comprise primer compositions containing 0-99% by weight, preferably 50-99% by weight, very particularly preferably 55-95% by weight, of solvents.

[0084] A further aspect of the invention is a method for bonding with adhesive systems, characterized by a) providing at least two identical or different lignocellulosic materials, b) optionally: producing an aqueous primer composition by adding water to a primer composition of the invention, c) applying the optional aqueous primer composition, d) optionally: interim storage of the primer-treated lignocellulosic materials for an exposure time, e) applying the NCO-containing adhesive composition to at least one lignocellulosic material, f) bringing together the at least two lignocellulosic materials, g) compressing the lignocellulosic materials, h) optionally: post-curing the bonded lignocellulosic materials by means of storage.

[0085] For method step c), it is possible to use primer compositions or aqueous primer compositions in the application volume of 1-500 g / m2, preferably 5-100 g / m2, more preferably 10-50 g / m2, based on the surface materials and / or boards (for example lamellas) and / or finger joints to be bonded. For lignocellulosic fibres and particles (for example wood shavings), it is possible to use 0.001-0.2 g of primer composition per g of lignocellulosic material.

[0086] Method steps c) and e) may optionally also be performed simultaneously by means of two separate application systems.

[0087] In the optional method step b), an aqueous primer composition is produced by adding water to a primer composition in accordance with Claims 1-2. The primer composition may contain 1-100% by weight of polyglycerol partial esters and / or polyglycerols. The content of polyglycerol partial esters and / or polyglycerol may however also be 50-100% by weight (concentrate) or 1-30% by weight (diluted primer composition). Depending on the concentration of this component, it is possible to produce an applicable primer composition by adding solvent, for example water.

[0088] Preferably, the primer compositions according to the invention are used in diluted form.

[0089] Adhesive systems for the production of lignocellulosic composite materials are thus also provided, comprising a) a primer composition b) a moisture-curing NCO-containing adhesive composition wherein the primer composition (diluted primer composition) comprises

[0090] 1-30% by weight of polyglycerol partial esters and / or polyglycerol 0-15% by weight of surfactants 55-99% by weight of solvents.

[0091] These primer compositions (diluted primer compositions) can be applied directly.

[0092] Preference is however given to using concentrates of the primer composition. These primer compositions (concentrates) can be applied directly to the composite materials or diluted prior to processing. 202400200 13

[0093] Adhesive systems for the production of lignocellulosic composite materials are thus also provided, comprising c) a primer composition d) a moisture-curing NCO-containing adhesive composition wherein the primer composition (concentrate) comprises

[0094] 50-100% by weight of polyglycerol partial esters and / or polyglycerol

[0095] 0-15% by weight of surfactants

[0096] 0-50% by weight of solvents.

[0097] For method step e) it is possible to use NCO-containing adhesive compositions of 90-350 g / m2, preferably 120-250 g / m2, more preferably 140-200 g / m2, based on the surface materials and / or boards (for example lamellas) and / or finger joints to be bonded. For lignocellulosic fibres and particles (for example wood shavings), it is possible to use 0.005-0.5 g of NCO-containing adhesive formulation per g of lignocellulosic material.

[0098] Method steps c) and e) may be performed by spraying, knife coating, dipping, brushing, passing through a primer or adhesive curtain or application using nozzles or cartridges.

[0099] Method steps d), g) and h) may optionally be carried out at elevated temperature, and step g) also at elevated pressure, in order to achieve a fast-curing and firm adhesive join.

[0100] For method step g), a pressure of 0.4-2 N / mm2, preferably 0.6-1 .4 N / mm2, may be used for surface bonding and narrow-side bonding, and a pressure of 5-15 N / mm2, preferably 7.5-10 N / mm2, for finger jointing.

[0101] For method steps d), g) and h), a temperature of 0-210°C, preferably 15-40°C, may be used, for example by means of a heated ambient atmosphere or temperature-controlled presses.

[0102] Also claimed are the cured adhesive systems comprising a primer composition and a moisture-curing NCO-containing adhesive composition.

[0103] In particular, the use of the adhesive system of the invention for the bonding of lignocellulosic materials is claimed.

[0104] Particular preference here is given to bondings of sawn timber, fibres, chips, boards, wood splints, veneers, parquet, cross-laminated timber, glue-laminated timber, laminated veneer lumber, solid wood panels, veneer plywood, I-joists, TJI joists, scrimber products and shavings.

[0105] The bonding of hardwoods, softwoods, grasses, beech woods, oak woods, sweet chestnut and other Fagaceae, ash and other Oleaceae, birch and other Betulaceae, eucalypts, robinia, bangkirai, teak, meranti, ekki, merbau, abachi, wenge and other tropical timbers, Salicaceae, Douglas fir, pines, larches and other Pinaceae, hinoki cypress, Chinese fir, Japanese cedar and other Cupressaceae, acetylated wood, bamboo, Miscanthus, rice straw, cereal straw and hemp shives is particularly preferably claimed here. 202400200 14

[0106] There is a broad field of application for the use of the adhesive systems of the invention. Bonded lignocellulosic materials are used in various use markets. For example in furniture construction, in structural glued laminated timber construction, in vehicles, in boat construction and in parquet and facades.

[0107] It has been found that the adhesive systems according to the invention are also suitable for the bonding of lignocellulosic materials with other materials, for example metal, plastics, in particular with foam materials, ceramics and glass.

[0108] Examples

[0109] All stated percentages relating to the compositions or formulations refer to % by weight based on the total weight of the respective composition, unless expressly stated otherwise.

[0110] Conditions for the production of the wood test specimens:

[0111] The bonded lignocellulosic hardwood and softwood materials were produced in accordance with standards DIN EN 14080 (2013) and DIN EN 302-1 (2017). Unsteamed beech and Douglas fir wood panels were used, the bulk density, wood moisture content, length, thickness and width of the beech wood boards being standards-compliant. The density of Douglas fir boards is not specified in the standard and was 0.50-0.60 g / cm3in the experiments shown.

[0112] Creation of the test specimens for the longitudinal tensile shear test:

[0113] The 130 x 150 x 5 mm panels were placed in a climatic chamber at a temperature of 18-22°C and a relative humidity of 60-70% for at least one week.

[0114] For the production of in each case up to 5 wood test specimens, two panels were bonded. For this, the panels were first pretreated using an airbrush application system with the specified amount of the primer solution or, for the reference, with the same amount of water. In the case of non-primed references, this step was skipped. After a wait time of 10 min, the specified amount of the 1 K-PUR adhesive composition (Loctite® HB S309 Purbond from Henkel AG & Co. KGaA, Germany) was applied and the wooden panels were placed one on top of the other and pressed together lightly.

[0115] This was followed by compression using a hydraulic press at various pressing pressures and pressing times at room temperature of 20-30°C, after which the bonded materials were stored for 7-14 days under normal climatic conditions. The test specimens were cut to size using a CNC router, by making two offset cuts at right angles to the wood fibre in accordance with the standard. In addition, the two outer sections parallel to the fibre direction were cut away at a distance of 7.5 mm from the edges and discarded.

[0116] Creation of the glue-laminated timber for the delamination and compressive shear tests:

[0117] For the delamination and compressive shear tests, glue-laminated timbers were produced from in each case six lamellas of beech or Douglas fir in accordance with DIN EN 14080 (2013). As in the production of the longitudinal tensile shear test specimens, the wood was prior to bonding conditioned in a climatic chamber and immediately before bonding pretreated using an airbrush application system with primer or 202400200 15 water (reference), with a chosen wait time of 10 min between application of primer and application of adhesive.

[0118] Aftertreatments A4:

[0119] The longitudinal tensile shear test specimens were treated in accordance with the aftertreatment A4 described in DIN EN 302-1 (2017).

[0120] For samples in accordance with A4, the samples were first boiled in water for 6 hours and then, in a departure from the standard, immersed in cold water overnight instead of just for two hours, and measured wet in the longitudinal tensile shear test.

[0121] Procedure for the longitudinal tensile shear test:

[0122] The test specimens were clamped parallel to the direction of stress in the clamping jaws of the tensile testing machine at a distance of 90 mm and tested with the increase in load of 2.0 [± 0.5] kN / min specified in standard DIN 302-1 (2017). The test was judged to have ended when the test specimen fractured. The reported longitudinal tensile shear strength is the average value of the determined longitudinal tensile shear strengths of the tested test specimens. Test specimens that were significantly twisted and were unable to be clamped in the jaws without generating substantial stress in the adhesive join at right angles to the fibre direction were not included in the calculation of the average value. Such test specimens often already delaminate before the longitudinal tensile shear test while being clamped in the clamping jaws.

[0123] The values for the longitudinal tensile shear test are reported in N / mm2. The higher the value, the better the adhesive joins.

[0124] Procedure for the compressive shear tests:

[0125] For the compressive shear tests, five test pieces having a width of 50 nm and a thickness of 40 mm were taken from each of the two sides of the glue-laminated timber in accordance with the description in DIN EN 14080 (2013) Appendix D. The compressive shear tests were then carried out according to the method described in DIN 52187 (1979). The reported compressive shear strength is the average value of the 10 test pieces.

[0126] The values for the compressive shear test are reported in N / mm2. The higher the value, the better the adhesive joins.

[0127] Procedure for the delamination tests:

[0128] A delamination test simulates the weathering conditions to which timber components are exposed and evaluates what percentage of the adhesive joins are no longer intact after the test. For the delamination tests, at least two test pieces were sawn from the glue-laminated timber (left and right, optionally middle) and subjected to a test cycle in accordance with DIN EN 14080 (2013) Annex C Method B. This consists of a watering phase (30 min, 15-30 kPa reduced pressure, 120 min 600-700 kPa overpressure) and a drying phase (several hours at 70 ± 5°C and a relative humidity of 9 ± 1% with an air flow of 202400200 16

[0129] 2.5 ± 0.5 m / s). The delamination is then evaluated using a microscope as described in EN 14080 (2013). The reported delamination values are the average delamination of all adhesive joins in all test pieces (“average delamination value of all adhesive joins”).

[0130] The values for the delamination tests are expressed in %. The lower the value, the better the adhesive joins.

[0131] Determination of wood tear-out:

[0132] After carrying out the longitudinal tensile shear test, the wood tear-out is in each case determined by analysing the two test specimen fragments using a Keyence VR-5000 optical 3D profilometer. In this test, raised areas or depressions respectively higher or deeper than 0.1 mm are considered to be wood tearout. The wood tear-out after carrying out the compressive strength test is determined by microscopy. The reported wood tear-outs are in each case average values of all wood tear-outs of the respective test piece and is reported in %. The higher the value, the better.

[0133] Other measurement methods

[0134] The acid value (AV) is determined according to the titration method DIN EN ISO 2114. The unit for the reported AV is mg KOH / g of polymer.

[0135] The average degree of polymerization of the polyglycerols N is calculated via its hydroxyl value (OHV, in mg KOH / g) according to the formula N = (112200 - 18 OHV) / (74 OHV - 56 100).

[0136] Suitable methods for determining the hydroxyl value (OHV) are in particular those according to DGF C-V 17 a (53), Ph. Eur. 2.5.3 Method A and DIN 53240.

[0137] The OHV is determined in accordance with the standard method DGF C-V17a by acetylation of the alcohol function with an excess of acetic anhydride in pyridine and back-titration with KOH solution. The unit for the OHV is mg KOH / g of polymer.

[0138] The saponification value (SV) indicates how many milligrams of potassium hydroxide (KOH) is required to completely saponify one gram (1 g) of fat. In accordance with EN ISO 3657: 20213. The unit for the SV is mg KOH / g of substance.

[0139] Materials

[0140] The NCO-containing adhesive composition (1 K-PUR) Loctite® HB S309 Purbond from Henkel AG & Co. KGaA, Germany that is used is commercially available.

[0141] The tested primer compositions were obtained by dilution of primers with water. The noninventive primers are either commercially available or were synthesized according to established methods.

[0142] Noninventive primers:

[0143] POE(40) monostearate (from about 1% and above the compound is no longer water-soluble, which was the reason for using a 0.5% solution, from TCI Deutschland GmbH, Germany)

[0144] TEGO® Humectant 7000 (POE alcohol, from Evonik Industries AG, Germany) 202400200 17

[0145] Loctite PR 3105 Purbond® (from Henkel AG & Co. KGaA, Germany)

[0146] Break-Thru® S 301 (surface-active siloxane derivative, from Evonik Industries AG, Germany) Surfynol® 485 (acetylenediol derivative, from Evonik Industries AG, Germany)

[0147] POE 2,4,7,9-tetramethyl-5-decyne-4,7-diol (Surfynol® AS 5040, acetylenediol derivative, from Evonik Industries AG, Germany)

[0148] Surfynol® AS 5060 (acetylenediol derivative, from Evonik Industries AG, Germany) Surfynol® AS 5160 (alkyl sulfosuccinate, from Evonik Industries AG, Germany) TEGO® Care PS MB (methylglucose sesquistearate, from Evonik Industries AG, Germany) Sodium lauryl sulfate (SDS, from Merck KGaA, Germany)

[0149] Poloxamer 188 (poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)) Kolliphor® P 188, OHV = OHV = 14 mg KOH / g, from Merck KGaA, Germany) Sodium dodecylbenzenesulfonate (SDBS, from Merck KGaA, Germany)

[0150] POE(5) 1-undecanyl ether (commercially available or produced by synthesis described below) POE(7) monooleate (commercially available or produced by synthesis described below) POE(34) glyceryl stearate (mono / diethoxy and mono / distearate) (produced by synthesis described below)

[0151] The prior art includes various documents in which alcohols, carboxylic acids or esters are used as starter compounds for the alkoxylation reaction. A good overview of polyoxyalkylenes and methods for preparing polyoxyalkylenes is given for example in “N. Schonfeldt, Surface Active Ethylene Oxide Adducts, Pergamon Press, 1969”. The alkoxylated compounds used in the context of this invention, where they were not acquired commercially, were prepared according to the following method:

[0152] In the first step, a starter compound is reacted using a catalyst with epoxides, for example ethylene oxide or propylene oxide or any desired mixtures of these epoxides. For example, in the case of POE(5) 1- undecanyl ether for the production of primers, 1 part of 1 -undecanol was initially charged as starter compound and 5 parts of ethylene oxide were used as epoxide. “Part” refers here to the relative molar proportion, not to the mass fraction. Catalysts used for the alkoxylation reaction are the alkaline catalysts known to those skilled in the art, such as potassium hydroxide, potassium hydroxide solution, sodium methoxide or potassium methoxide, or double metal cyanide compounds. Starter compound and catalyst are initially charged in the reactor at the start of the process prior to the metered addition of epoxide, wherein the amount of catalyst must be set so as to ensure sufficient catalytic activity for the process. The reaction temperature in the first step is preferably 80 to 220°C. The pressure in the first step is preferably 0.5 bar to 20 bar (absolute).

[0153] The epoxy monomers may be used in pure or mixed form, with the result that homopolymers or random copolymers are obtained. After the metered addition of a first monomer or a monomer mixture, further monomer may be metered in, with the result that block structures are obtained. A further epoxide may also be metered continuously over time into an epoxide already present in the reaction mixture, so as to give rise to an increasing concentration gradient of the continuously added epoxide. The relationships between metered addition and product structure are known to those skilled in the art.

[0154] The end of the epoxide addition is typically followed by a period of further reaction to allow the reaction to proceed to completion. The further reaction can for example be carried out by continued reaction under 202400200 18 reaction conditions (i.e. maintenance for example of the temperature and of the pressure) without addition of reactants. Preferably, the further reaction is carried out with thorough mixing of the reaction mixture, especially with stirring.

[0155] In an optional second step, residual monomers are removed in a vacuum distillation and, if required, the reaction product is neutralized with an acid such as lactic acid, acetic acid, propionic acid or phosphoric acid, and the salts formed are optionally removed by filtration. In principle, it is also possible to perform further modifications, for example to add an additional esterification.

[0156] Inventive primer compositions:

[0157] Polyglyceryl-4 caprate

[0158] A mixture of 105.8 g of commercially available polyglycerol-4 for cosmetics use (Spiga Nord S.p.A; Italy) and 26.5 g of capric acid (99%) was heated to 240°C over the course of 3 h with stirring and introduction of N2 and the water formed was continuously distilled off until an acid value of < 2.0 mg KOH / g had been reached. The product obtained had an acid value (AV) of 0.5 mg KOH / g, a saponification value (SV) of 65 mg KOH / g and a hydroxyl value (OHV) of 790 mg KOH / g.

[0159] The average degree of polymerization N is 4.

[0160] Polyglycerol-3

[0161] Polyglycerol-3 (Spiga Nord S.p.A, Italy) is commercially available for cosmetics use.

[0162] The average degree of polymerization N is 3.2.

[0163] The polyglycerol-3 had a hydroxyl value (OHV) of 1150 mg KOH / g.

[0164] Example 1 : Longitudinal tensile shear test in accordance with DIN EN 302-1 (2017) A4 of noninventive primers in comparison with inventive polyqlvceryl-4 caprate on beech wood

[0165] Substrate: Beech wood (Fagus sylvatica)

[0166] Primer composition: 20 g / m2

[0167] Adhesive: 200 g / m2Loctite Purbond® HB S309

[0168] Pressure: 1 .28 N / mm2 202400200 19

[0169] EP2928977A1 claims in general terms all adhesive systems having a primer constituent that either contains a polyol having a molecular weight below 5000 daltons and / or contains surface-active 202400200 20 compounds from the following list: surface-active siloxane derivatives, alkyl polyglucosides, alkoxylated fatty acids, alkoxylated alcohols, alkyl sulfosuccinates, acetylenediol derivatives. Example 1 shows that such a broad substance class definition primarily includes compounds that are only poorly suitable, if at all, as primers, and that primers of the invention are superior to the structures from the broad substance class definition in their effect as primers in terms of adhesive join strength. In addition, primers of the invention are shown to be superior to polyethers with OHV < 30 from EP2848638B1 and to salts of dodecylbenzenesulfonic acid from WO03093385A2 in the longitudinal shear tests on beech wood carried out. The values in the longitudinal tensile shear strength for both polyglyceryl-4 caprate and polyglycerol- 3 are higher than the values for the prior art compounds tested in the comparative experiments. A further advantage over many of the structures tested in example 1 is that the primers of the invention are POE- free.

[0170] Example 2: Longitudinal tensile shear test in accordance with DIN EN 302-1 (2017) A4 of noninventive primers in comparison with inventive polyqlvceryl-4 caprate on Douglas fir wood Substrate: Douglas fir (Pseudotsuga menziesii) Primer composition: 20 g / m2

[0171] Adhesive: 200 g / m2Loctite Purbond® HB S309 Pressure: 1 .28 N / mm2

[0172] Example 2 shows that, in the longitudinal shear tests carried out not only on beech wood (a hardwood, see example 1) but also on Douglas fir softwood, a primer composition of the invention improves bonding compared to the reference without primer active substance and compared to the use of POE-containing primers (as described in EP2928977). The value for the longitudinal tensile shear strength is significantly higher for the polyglyceryl-4 caprate of the invention and thus better than the values for the comparative tests.

[0173] Example 3: Delamination test according to DIN EN 14080 (2013) Method B with Douglas fir and beech Substrate: Douglas fir wood (Pseudotsuga menziesii) and beechwood (Fagus sylvatica) 202400200 21

[0174] Primer: 20 g / m2

[0175] Adhesive: 200 g / m2Loctite Purbond® HB S309

[0176] Pressure: 1 .2 N / mm2

[0177] Pressing time: 150 min

[0178] The comparative examples show that the delamination values for beech are very high, outside the DIN standard. For Douglas fir, the value without primer was likewise far outside the DIN standard.

[0179] Consequently, delamination experiments with POE 2,4,7,9-tetramethyl-5-decyne-4,7-diol (1 % aqueous solution) on Douglas fir were not carried out.

[0180] DIN EN 14080 (2013) specifies that a maximum of 4% delamination is permitted in the first run in the delamination test according to Method B. Among the experiments shown, this is achieved only with the primer of the invention, both for beech and for Douglas fir.

[0181] Example 4: Compressive shear test according to DIN EN 14080 (2013) on bonded beech test specimens

[0182] Substrate: Beech wood (Fagus sylvatica)

[0183] Primer composition: 20 g / m2

[0184] Adhesive: 200 g / m2Loctite Purbond® HB S309

[0185] Pressure: 1 .2 N / mm2

[0186] Pressing time: 150 min 202400200 22

[0187] Example 4 shows that a primer composition of the invention is also advantageous in the pressure shear tests carried out compared to the use of POE-containing primers. The higher the wood tear-off, the more resistant the adhesive join, since breakage results in the test specimens breaking in the wood and not in the adhesive join.

Claims

202400200 23Claims1. Adhesive system for the production of lignocellulosic composite materials, comprising a) a primer composition b) a moisture-curing NCO-containing adhesive composition wherein the primer composition comprises:1-100% by weight of polyglycerol partial esters and / or polyglycerol, preferably 1-30% by weight0-15% by weight of surfactants0-99% by weight of solvents, preferably 55-95% by weight.

2. Adhesive system according to Claim 1 , characterized in that the polyglycerols and the polyglycerols present in the polyglycerol partial esters have an average degree of polymerization N of 1 .1 to 20, preferably 2.5 to 16 and very particularly preferably 2.6 to 12.

3. Adhesive systems according to Claim 1 , characterized in that the polyglycerols or polyglycerol partial esters have a hydroxyl value of 10-1400 mg KOH / g.

4. Adhesive systems according to Claim 1 , characterized in that the polyglycerol partial esters contain structures of general formula (I)wherein the repeat units may be arranged in any desired order, where k + I = 1 .1-20, preferably 2.5-16, more preferably 2.6-12, andR1= each independently identical or different H, -C(=O)-R2, -C(=O)-R3or -R3radicals, where R2= each independently identical or different alkyl radicals or alkenyl radicals having 1 to 21 carbon atoms or aryl radicals having 6-18 carbon atoms, preferably alkyl and alkenyl radicals having 5-17 carbon atoms, more preferably alkyl radicals having 5-15 carbon atoms, andR3= each independently identical or different radicals composed of 1-18 bridging methylene units -CH2- and / or -CH(CH2OH)- units, wherein in structure (I) on average at least 4% of the radicals R1must be different from H and preferably at least one radical is -C(=O)-R2or -C(=O)-R3.202400200 245. Adhesive systems according to Claim 1 , characterized in that the polyglycerol partial esters are obtained by esterification of polyglycerol with at least one fatty acid or diacid or polyacids or acyl donors derived therefrom.

6. Adhesive systems according to Claim 1 , characterized in that the surfactants are selected from the group of water-soluble surfactants, water-dispersible surfactants and mixtures thereof.

7. Adhesive systems according to Claim 1 , characterized in that the solvent for the primer composition is preferably water.

8. Adhesive systems according to Claim 1 , characterized in that the moisture-curing NCO- containing adhesive composition is characterized in that- it contains prepolymers formed by reaction of polyether polyols with aromatic isocyanates having two or more NCO functionalities and that- it has an NCO content of 1-28% by weight, preferably of 1-20% by weight, more preferably of 10-20% by weight.

9. Adhesive systems according to Claim 1 , characterized in that the moisture-curing NCO- containing adhesive composition is characterized in that it comprises polymeric diphenylmethane diisocyanate (pMDI) as main component and has an NCO content of 28- 32% by weight.

10. Adhesive system according to Claim 1 , characterized in that the NCO-containing adhesive composition comprises crosslinkers, fillers, catalysts, stabilizers, defoamers, antioxidants, viscosity modifiers, activators, further auxiliaries and mixtures thereof.11 . Adhesive system for the production of lignocellulosic composite materials, comprising a) a primer composition b) a moisture-curing NCO-containing adhesive composition wherein the primer composition comprises:- 1-100% by weight of polyglyceryl-4 caprate, polyglyceryl-3 caprate, polyglycerol-4 or polyglycerol-3, preferably 1-30% by weight- 0-15% by weight of surfactants- 0-99% by weight of solvents, preferably 5-95% by weight.

12. Method for bonding with adhesive systems according to Claim 1 , characterized by a) providing at least two identical or different lignocellulosic materials, b) optionally: producing an aqueous primer composition by adding water to a primer composition according to Claim 1 ,202400200 25 c) applying the optional aqueous primer composition according to Claim 1 , d) optionally: interim storage of the primer-treated lignocellulosic materials for an exposure time, e) applying the NCO-containing adhesive composition to at least one lignocellulosic material, f) bringing together the at least two lignocellulosic materials, g) compressing the lignocellulosic materials, h) optionally: post-curing the bonded lignocellulosic materials by means of storage.

13. Use of the adhesive systems according to Claim 1 for the bonding of lignocellulosic materials, selected from the group of hardwoods, softwoods, grasses, beech woods, oak woods, sweet chestnut and other Fagaceae, ash and other Oleaceae, birch and other Betulaceae, eucalypts, robinia, bangkirai, teak, meranti, ekki, merbau, abachi, wenge and other tropical timbers, Salicaceae, Douglas fir, pines, larches and other Pinaceae, hinoki cypress, Chinese fir, Japanese cedar and other Cupressaceae, acetylated wood, bamboo, Miscanthus, rice straw, cereal straw and hemp shives.

14. Use of the adhesive systems according to Claim 13 in the bondings of sawn timber, fibres, chips, boards, wood splints, veneers, parquet, cross-laminated timber, glue-laminated timber, laminated veneer lumber, solid wood panels, veneer plywood, I-joists, TJI joists, scrimber products and shavings.

15. Use of the adhesive systems according to Claim 14 in furniture construction, structural glued laminated timber construction, boat construction, vehicles and facades.

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