Three-component polyurethane composition having a dynamically settable pot life

Abstract

The present invention relates to a three-component polyurethane composition suitable as a laminating glue, consisting of three components to be mixed during use, wherein the first component and the second component each comprise at least one polyol having an OH functionality in the range of 1.5 to 4 and having an average molecular weight (number average) Mn in the range of 250 to 15,000 g / mol, and at least one metal catalyst for the reaction of hydroxyl groups and isocyanate groups, said metal catalyst being able to form thio complexes, and at least one compound which has at least one thiol group, the molar ratio of all thiol groups of the at least one compound to all metal atoms of the at least one metal catalyst being between 1:1 and 250:1 in each of the first component and the second component, and the third component comprises at least one polyisocyanate, characterized in that the amount of metal catalyst contained in the first component is at least 1.5 times the amount of metal catalyst contained in the second component, with respect to the molar amount of metal atoms of the metal catalyst in each component. Such a composition allows the pot life to be dynamically set as desired, within certain limits, during the gluing process and makes it possible to achieve multi-layer adhesive bonds with a different pot life for each adhesive layer and with subsequent quick curing of the composition. The composition according to the invention is particularly suitable as a laminating glue for producing composite materials and can be used at any ambient temperature.

Description

[0001] Three-component polyurethane composition with dynamically adjustable pot life

[0002] Technical field

[0003] The invention relates to the field of three-component polyurethane compositions suitable as laminating adhesives, as well as a method for bonding at least three substrates layer by layer.

[0004] State of the art

[0005] Cross-laminated timber (CLT), also known as multi-layer solid wood panels, is an increasingly sought-after raw material in construction and industry. It is typically manufactured by bonding and pressing thin layers of wood together, usually as three-layer panels, and is superior to solid wood panels of the same thickness in terms of mechanical properties, dimensional stability, and manufacturing costs. Various laminating adhesives are used in the process. Traditionally, these include melamine resins such as melamine-phenol-formaldehyde resins (MPF) or melamine-urea-formaldehyde resins (MUF), as well as one-component or two-component polyurethane adhesives. Melamine resins have the significant disadvantage of containing formaldehyde, which is highly problematic from a toxicological perspective, especially for residential applications.In contrast, single-component polyurethane compounds require very long pressing times and are therefore not preferred for industrial applications. Two-component polyurethane compounds based on polyols and polyisocyanates have been used for a long time. Compared to single-component, moisture-curing polyurethane compounds, two-component polyurethane compounds have the advantage that they cure quickly after mixing and can therefore absorb and transmit higher forces after a short time.

[0006] For use as laminating adhesives, for example in the production of plywood panels, high demands are placed on such compositions with regard to strength and adhesion forces, since these adhesives are used for the production of composite elements, e.g., sandwich panels, and various substrates must be bonded together permanently and over a large area. In particular, such compositions require good mechanical properties in their cured state, such as sufficient tensile strength with suitable moduli of elasticity, to ensure the stability of the composite materials even under thermal or mechanical stress. This is especially challenging with substrates that have different coefficients of thermal expansion. Furthermore, the adhesive performance of the adhesive must remain constant over the service life of the composite element. Additionally, it is important to note that, for example,In industrial manufacturing, it is desirable for such adhesives to have a sufficiently long pot life for the large-area application required in the production of composite elements, but to cure as quickly as possible thereafter, thus reducing cycle times. Furthermore, the pot life and curing times should ideally be adjustable to the desired manufacturing process to enable efficient, automated application.

[0007] To achieve the desired mechanical properties and, above all, particularly rapid curing, high proportions of isocyanates are advantageous in such compositions. These isocyanates are present in one of the two components as free or polymer-bound polyisocyanates and cure upon mixing with the other component, which contains polyols, forming a polymeric network. However, a high isocyanate content leads to problems. Especially when using crosslinking catalysts, which are essential for selective, optimal crosslinking and curing, such two-component systems become almost uncontrollably fast, and the pot lives are far too short for use as laminating adhesives. Furthermore, the laminating adhesives are intended to bond multiple layers of substrates to form a composite material, with the laminate being pressed after completion of the multilayer bonding process.The compression process must take place within the pot life of all applied adhesive layers to ensure a cleanly bonded composite element. With two-component polyurethane compounds, the pot life is constant and must be set long enough for multi-layer bonding to allow all layers to be applied and compression to be carried out within the pot life of the first adhesive layer. However, the compression time must typically be at least as long as the pot life. With a constant pot life across all adhesive layers, this leads to undesirably long compression times, as the pot life of the last applied adhesive layer determines the compression time. To address this problem, three-component polyurethane compounds have been developed, which are particularly suitable for multi-layer lamination bonding.

[0008] An example of such a process is disclosed in WO 2018 / 134476 A1. This document discloses an adhesive bonding process for multilayer bonding, using two different adhesive components with different pot lives and a hardener component. Computer-controlled dosing of the three components allows for a different pot life to be set for each adhesive layer by adjusting the mixing ratio of the two adhesive components, thus accelerating the entire lamination process. However, this publication does not disclose details about the chemical composition of the adhesive and hardener components, except that they can be polyurethane-based. Not all polyurethane adhesives are readily suitable for such a process. A significant problem, particularly in industrial lamination processes, is the high sensitivity of common polyurethane adhesives to moisture, especially relative humidity.This is particularly problematic because in industrial lamination, the adhesives are used in very thin (e.g., 100 pm to 1 mm) but large-area (up to several m) layers. 2 Layers are applied, resulting in a large interface with the ambient air. At relative humidity levels above 50%, problems arise in large-area, thin-film lamination applications when two-component polyurethanes are used as adhesives. These adhesives can harden uncontrollably, sometimes forming bubbles and failing to adhere sufficiently to the substrate layers, or the catalyst system can be deactivated by the moisture. Furthermore, the storage stability of these two-component compounds is often insufficient, as the catalytic activity changes over time. This leads to process disruptions, particularly in industrial, automated lamination processes involving large-area, thin-film adhesive application.

[0009] A further, more concrete example of a three-component polyurethane composition specifically for laminating bonds is disclosed in WO 2023 / 031304 A1. This publication discloses three-component polyurethane compositions that have been optimized with regard to the aforementioned problems. The compositions disclosed in this publication comprise a polyol component, which contains a thiol compound in addition to a polyol; a catalyst component, which comprises a curing catalyst and a desiccant; and an isocyanate component. By separating the three main components—polyol, isocyanate, and catalyst—and using the desiccant, the problems described above concerning moisture sensitivity and storage stability can be largely solved. However, this publication does not describe a laminating process that would allow for flexible adjustment of the pot life across the individual adhesive layers.The use of the learned thiol compound can extend the pot life of the entire adhesive process and simultaneously shorten the pressing time, but only within narrow limits and not always to the desired extent, compared to a two-component polyurethane composition, since the pot life of all individual adhesive layers remains identical.

[0010] WO 2019 / 013917 A1 discloses a three-component polyurethane composition with two polyol components, each containing a latent organometallic catalyst and a blocked cyclic amidine catalyst. In some embodiments, the organometallic catalyst may be a dialkyltin dimercaptide complex.

[0011] Therefore, there is a need for a polyurethane-based laminating adhesive that allows a dynamically adjustable pot life throughout the entire bonding process, with the pot life becoming shorter with each adhesive layer, and which can be dynamically adjusted based on parameters such as the ambient temperature, while enabling extremely rapid curing after an exceptionally short pressing time following completion of the bonding process.

[0012] Description of the invention

[0013] The object of the present invention is therefore to provide a three-component polyurethane composition that cures very quickly to a mechanically excellent mass suitable as a laminating adhesive, but at the same time has a sufficiently long pot life, dynamically adjustable across the individual adhesive layers, so that it can be processed without difficulty and pressed in an extremely short time, thus allowing exceptionally fast cycle times that are independent of the ambient temperature. Surprisingly, this object is achieved with the three-component polyurethane composition according to claim 1. It consists of three individually packaged components that are mixed only before or during application.The first and second components each comprise at least one polyol, a compound with at least one thiol group, and at least one metal catalyst, with the first component containing at least 1.5 times the amount of catalyst as the second component. The third component comprises at least one polyisocyanate. The pot life of the adhesive layers can be dynamically adjusted by changing the mixing ratio of the first and second components. This enables a process for bonding at least three substrates connected by adhesive layers, which can be optimized to a high degree with respect to the required pressing times at the end of the bonding process and thus the required cycle times, regardless of the ambient temperature.

[0014] Further aspects of the invention are the subject of further independent claims. Particularly preferred embodiments of the invention are the subject of dependent claims.

[0015] Ways to implement the invention

[0016] The present invention relates to a polyurethane composition suitable as a laminating adhesive, comprising three components A-1, A-2 and B which are to be mixed during application; wherein the first component A-1 and the second component A-2 each

[0017] - at least one polyol P with an OH functionality in the range of 1.5 to 4 and a number-mean molecular weight M n in the range of 250 to 15,000 g / mol, as well as

[0018] - at least one metal catalyst K for the reaction of hydroxyl groups and isocyanate groups, which can form thio complexes, as well as

[0019] - comprising at least one compound T comprising at least one thiol group; wherein the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K in the first component A-1 and in the second component A-2 is between 1:1 and 250:1 respectively; and the third component B

[0020] - comprising at least one polyisocyanate I; characterized in that the first component A-1 contains at least 1.5 times the amount of metal catalyst K as is contained in the second component A-2, based on the molar amount of metal atoms of the metal catalyst K in the respective component.

[0021] The prefix "Poly" in substance names such as "Polyol", "Polyisocyanate", "Polyether" or "Polyamine" indicates in this document that the respective substance formally contains more than one of the functional groups appearing in its name per molecule.

[0022] In this document, the term "polymer" encompasses, on the one hand, a group of chemically uniform macromolecules that differ in degree of polymerization, molar mass, and chain length, and which are produced by a polymerization reaction (polymerization, polyaddition, polycondensation). On the other hand, the term also includes derivatives of such a group of macromolecules from polymerization reactions; that is, compounds obtained by changes, such as additions or substitutions, of functional groups on given macromolecules, and which may be chemically uniform or chemically heterogeneous. Furthermore, the term also includes so-called prepolymers, that is, reactive oligomeric pre-adducts whose functional groups are involved in the construction of macromolecules.

[0023] The term "polyurethane polymer" encompasses all polymers produced using the so-called diisocyanate polyaddition process. This also includes polymers that are almost or entirely free of urethane groups. Examples of polyurethane polymers are polyether polyurethanes, polyester polyurethanes, polyether polyureas, polyureas, polyester polyureas, polyisocyanurates, and polycarbodiimides.

[0024] In this document, "molecular weight" refers to the molar mass (in grams per mole) of a molecule or molecular residue. "Mean molecular weight" refers to the number mean Mn of a polydisperse mixture of oligomeric or polymeric molecules or molecular residues, which is usually determined by gel permeation chromatography (GPC) against polystyrene as a standard. "Room temperature" in this document refers to a temperature of 23 °C. Weight percent, abbreviated wt%, denotes the mass fraction of a component of a composition, based on the total composition, unless otherwise specified. The terms "mass" and "weight" are used synonymously in this document.

[0025] A "primary hydroxyl group" is an OH group that is bonded to a carbon atom with two hydrogens.

[0026] In this document, "pot life" refers to the time within which the polyurethane composition according to the invention, after mixing the three components at a specific temperature, for example 20°C or as defined for this pot life, reaches a complex viscosity of 1000 Pa s, measured on a thermostatically controlled plate-plate rheometer MCR 302 (Anton Paar) with a plate diameter of 25 mm and a plate spacing of 1 mm at an angular frequency of 6 rad s. -1 (0.95 Hz). Once this viscosity value is reached, the viscosity of the composition increases very rapidly due to the increasingly rapid curing process. Any compression of bonded substrates must begin within the pot life to ensure a well-bonded composite element.

[0027] In this document, "pressing time" refers to the time required to press two substrates of a composite material together until the curing and adhesion development of the polyurethane composition applied between them has progressed sufficiently for the bond to possess a defined initial strength suitable for movement, in particular a tensile strength of 1 MPa. Typically, the pressing time corresponds to the pot life of the slowest curing applied adhesive layer, plus the remaining pot life of that layer. Since pressing must commence while the pot life is still within the period of time remaining, the remaining pot life of the slowest adhesive layer is added to the total pot life when calculating the minimum pressing time.

[0028] In this document, "room temperature" is defined as a temperature of 23 °C.

[0029] A substance or composition is described as "storage-stable" or "storable" if it can be stored at room temperature in a suitable container for a longer period of time, typically at least 3 months up to 6 months or more, without its application or usage properties, in particular its viscosity and crosslinking rate, changing to an extent relevant to its use.

[0030] All industry standards and norms mentioned in the document refer to the versions valid at the time of the initial application.

[0031] The first component A-1 and the second component A-2

[0032] The first component A-1 and the second component A-2 each comprise at least one polyol P with an OH functionality in the range of 1.5 to 4 and a number-mean molecular weight M nin the range of 250 to 15,000 g / mol, and at least one metal catalyst K for the reaction of hydroxyl groups and isocyanate groups, which can form thio complexes, and at least one compound T which has at least one thiol group, wherein the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K in the first component A-1 and in the second component A-2 is between 1 :1 and 250:1.

[0033] Furthermore, the first component A-1 contains at least 1.5 times the amount of metal catalyst K as is contained in the second component A-2, based on the molar amount of metal atoms of the metal catalyst K in the respective component.

[0034] In principle, the first component A-1 and the second component A-2 can have a similar or even identical structure, as long as the first component A-1 contains a higher proportion of metal catalyst K than the second component A-2, as defined. Preferably, however, further differences exist, particularly in the respective amount of compound T. This is described in more detail below.

[0035] The first component A-1 and the second component A-2 each initially contain at least one polyol P with an OH functionality in the range of 1.5 to 4 and an average molecular weight in the range of 250 to 15,000 g / mol.

[0036] Suitable polyols P are in principle all common polyols for the production of

[0037] Polyurethane polymers. Particularly suitable are polyether polyols, polyester polyols, poly(meth)acrylate polyols, polybutadiene polyols, polycarbonate polyols, and mixtures of these polyols.

[0038] Polyether polyols, also called polyoxyalkylene polyols or oligoetherols, are particularly suitable if they are polymerization products of ethylene oxide, 1,2-propylene oxide, 1,2- or 2,3-butylene oxide, oxetane, tetrahydrofuran, or mixtures thereof, optionally polymerized with the aid of a starter molecule with two or more active hydrogen atoms such as water, ammonia, or compounds with several OH or NH groups such as 1,2-ethanediol, 1,2- and 1,3-propanediol, neopentyl glycol, diethylene glycol, triethylene glycol, the isomeric dipropylene glycols and tripropylene glycols, the isomeric butanediols, pentanediols, hexanediols, heptanediols, octanediols, nonanediols, decanediols, undecanediols, 1,3- and 1 ,4-Cyclohexandimethanol, Bisphenol A, hydrogenated Bisphenol A, 1 ,1 ,1-Trimethylolethane, 1 ,1 ,1-Trimethylolpropane, Glycerol, Aniline, and mixtures of the aforementioned compounds.Both polyoxyalkylene polyols with a low degree of unsaturation (measured according to ASTM D-2849-69 and expressed in milliequivalents of unsaturation per gram of polyol (mEq / g)), produced for example using so-called double metal cyanide complex catalysts (DMC catalysts), and polyoxyalkylene polyols with a higher degree of unsaturation, produced for example using anionic catalysts such as NaOH, KOH, CsOH or alkali alcoholates, can be used.

[0039] Particularly suitable are polyoxyethylene polyols and polyoxypropylene polyols, especially polyoxyethylene diols, polyoxypropylene diols, polyoxyethylene triols, and polyoxypropylene triols. Polyoxyethylene triols and polyoxypropylene triols, especially polyoxypropylene triols, are preferred.

[0040] Particularly suitable are polyoxyalkylene diols or polyoxyalkylene triols with a degree of unsaturation lower than 0.02 mEq / g and with a molecular weight in the range of 1,000 to 15,000 g / mol, as well as polyoxyethylene diols, polyoxyethylene triols, polyoxypropylene diols and polyoxypropylene triols with a molecular weight of 400 to 15,000 g / mol.

[0041] Also particularly suitable are so-called ethylene oxide-terminated ("EO-endcapped," ethylene oxide-endcapped) polyoxypropylene polyols. These are special polyoxypropylene polyoxyethylene polyols obtained, for example, by further alkoxylating pure polyoxypropylene polyols, especially polyoxypropylene diols and triols, after completion of the polypropoxylation reaction with ethylene oxide, thereby giving them primary hydroxyl groups. Polyoxypropylene polyoxyethylene diols and polyoxypropylene polyoxyethylene triols, especially polyoxypropylene polyoxyethylene triols, are preferred in this case.

[0042] Also suitable are hydroxyl group terminated polybutadiene polyols, such as those produced by polymerization of 1,3-butadiene and allyl alcohol or by oxidation of polybutadiene, as well as their hydrogenation products.

[0043] Styrene-acrylonitrile grafted polyether polyols, such as those commercially available under the trade name Lupranol® from Elastogran GmbH, Germany, are also suitable.

[0044] Polyester polyols are particularly suitable if they bear at least two hydroxyl groups and are produced by known processes, in particular the polycondensation of hydroxycarboxylic acids or the polycondensation of aliphatic and / or aromatic polycarboxylic acids with dihydric or polyhydric alcohols.

[0045] Particularly suitable are polyester polyols produced from dihydric to trihydric alcohols such as 1,2-ethanediol, diethylene glycol, 1,2-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, glycerol, 1,1,1-trimethylolpropane, or mixtures of the aforementioned alcohols with organic dicarboxylic acids or their anhydrides or esters such as succinic acid, glutaric acid, adipic acid, trimethyladipic acid, cortic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic acid, fumaric acid, dimer fatty acid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, dimethyl terephthalate, hexahydrophthalic acid, trimellitic acid, and trimellitic anhydride, or mixtures of the aforementioned acids, as well as polyester polyols made from Lactones such as £-caprolactone.

[0046] Polyester diols are particularly suitable, especially those produced from adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, dimer fatty acid, phthalic acid, isophthalic acid, and terephthalic acid as dicarboxylic acids, or from lactones such as α-caprolactone, and from ethylene glycol, diethylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol, dimer fatty acid diol, and 1,4-cyclohexanedimethanol as dihydric alcohols. Polycarbonate polyols particularly suitable are those obtained by reacting, for example, the alcohols mentioned above (used in the synthesis of polyester polyols) with dialkyl carbonates such as dimethyl carbonate, diaryl carbonates such as diphenyl carbonate, or phosgene. Polycarbonates obtained from the copolymerization of CO₂ with epoxides such as ethylene oxide and propylene oxide are also suitable. Polycarbonate diols, especially amorphous polycarbonate diols, are particularly suitable.

[0047] Other suitable polyols are poly(meth)acrylate polyols.

[0048] Also suitable are polyhydroxy functional fats and oils, for example natural fats and oils, especially castor oil, or so-called oleochemical polyols obtained by chemical modification of natural fats and oils, such as epoxy polyesters or epoxy polyethers obtained by epoxidation of unsaturated oils and subsequent ring opening with carboxylic acids or alcohols, or polyols obtained by hydroformylation and hydrogenation of unsaturated oils.

[0049] Also suitable are polyols obtained from natural fats and oils through degradation processes such as alcoholysis or ozonolysis, followed by chemical bonding, for example by transesterification or dimerization, of the resulting degradation products or derivatives thereof. Suitable degradation products of natural fats and oils include, in particular, fatty acids and fatty alcohols, as well as fatty acid esters, especially methyl esters (FAME), which can be derivatized to hydroxy fatty acid esters, for example by hydroformylation and hydrogenation.

[0050] Also suitable are polyhydrocarbon polyols, also called oligohydrocarbonols, for example, polyhydroxy-functional ethylene-propylene, ethylene-butylene, or ethylene-propylene-diene copolymers, such as those manufactured by Kraton Polymers, USA; or polyhydroxy-functional copolymers of dienes such as 1,3-butanediene or diene mixtures and vinyl monomers such as styrene, acrylonitrile, or isobutylene; or polyhydroxy-functional polybutadiene polyols, for example, those produced by copolymerization of 1,3-butadiene and allyl alcohol, which may also be hydrogenated. Also suitable are polyhydroxy-functional acrylonitrile / butadiene copolymers, such as those produced from epoxides or amino alcohols, and carboxyl-terminated acrylonitrile / butadiene copolymers, which are commercially available under the name Hypro® (formerly Hycar®) CTBN from Emerald Performance Materials, LLC, USA.

[0051] All the polyols mentioned have an average molecular weight of 250 to 15,000 g / mol, particularly 300 to 10,000 g / mol, preferably 350 to 7,500 g / mol, and most preferably 400 to 5,000 g / mol, and an average OH functionality in the range of 1.5 to 4, preferably 1.7 to 3.5, and most preferably 2.0 to 3.0. However, the composition may also contain proportions of monoyl groups (polymers with only one hydroxyl group).

[0052] Particularly suitable polyols are polyether polyols, especially polyoxyethylene polyol, polyoxypropylene polyol, and polyoxypropylene polyoxyethylene polyol, preferably polyoxyethylene diol, polyoxypropylene diol, polyoxyethylene triol, polyoxypropylene triol, polyoxypropylene polyoxyethylene diol, and polyoxypropylene polyoxyethylene triol. Of all those mentioned, the respective triols are particularly preferred.

[0053] In preferred embodiments, the polyol P comprises at least one polyether triol or a mixture of polyether triols.

[0054] The first component A-1 and the second component A-2 may each still contain at least one diol with two hydroxyl groups connected via a C2 to C9 carbon chain.

[0055] Particularly suitable are diols selected from the group consisting of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,3-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 2,4-pentanediol, 2-methyl-1,4-butanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 1,2-hexanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,2-octanediol, 3,6-octanediol. 2-Ethyl-1,3-hexanediol, 2,2,4-Trimethyl-1,3-pentanediol, 2-Butyl-2-ethyl-1,3-propanediol, 2,7-Dimethyl-3,6-octanediol, 1,4-Cyclohexanediol, 1,3-Cyclohexanedimethanol, and 1,4-Cyclohexanedimethanol. Diols selected from the group consisting of 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, and 1,9-nonanediol are particularly preferred. These diols are commercially readily available and enable polyurethanes with particularly high moduli of elasticity and low elongation after curing.

[0056] In addition to the aforementioned polyols P and diols, small amounts of other low-molecular-weight dihydric or polyhydric alcohols, such as diethylene glycol, triethylene glycol, the isomeric dipropylene and tripropylene glycols, the isomeric decanediols and undecanediols, hydrogenated bisphenol A, dimeric fatty alcohols, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, glycerol, pentaerythritol, sugar alcohols such as xylitol, sorbitol, or mannitol, sugars such as sucrose, other higher-molecular-weight alcohols, low-molecular-weight alkoxylation products of the aforementioned dihydric and polyhydric alcohols, and mixtures of the aforementioned alcohols may also be used. Furthermore, polyols containing other heteroatoms, such as methyldiethanolamine or thiodiglycol, may also be present.

[0057] Component A-1 preferably contains 20 to 80 wt.%, preferably 30 to 70 wt.%, in particular 40 to 60 wt.%, polyol P, based on component A-1.

[0058] Component A-2 preferably contains 20 to 80 wt.%, preferably 30 to 70 wt.%, in particular 40 to 60 wt.%, polyol P, based on component A-2.

[0059] The first component A-1 and the second component A-2 each contain at least one compound T having at least one thiol group. Suitable compounds are those that have at least one thiol or mercapto group and that can be formulated according to the invention. A thiol group is understood here to be an -SH group bonded to an organic residue, for example, an aliphatic, cycloaliphatic, or aromatic carbon residue.

[0060] Compounds with 1 to 6, particularly 1 to 4, and most preferably 1 or 2 thiol groups are preferred. Compounds with one thiol group have the advantage that no complexes with the metal catalyst K, which tend to be sparingly soluble, are formed, and the pot life and open time can be adjusted with particular precision. Compounds with two or more thiol groups have the advantage that the mechanical properties of the composition are improved after curing.

[0061] Suitable compounds T with a thiol group are, for example, alkyl mercaptoacetates (alkyl thioglycolates), in particular methyl thioglycolate and isooctyl thioglycolate, 3-mercaptopropyltrialkoxysilanes, in particular 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane, 3-mercapto-1,2-propanediol, 2-mercaptotoluimidazole or 2-mercaptobenzothiazole.

[0062] Suitable compounds T with more than one thiol group are, for example, ethylene glycol di(3-mercaptopropionate), ethylene glycol dimercaptoacetate, trimethylolpropane tri(3-mercaptopropionate), dipentaerythritol hexa(3-mercaptopropionate), 2,3-dimercapto-1,3,4-thiadiazole or pentaerythritol tetrakis(3-mercaptopropionate).

[0063] The compound T is preferably selected from the group consisting of ethylene glycol di(3-mercaptopropionate), ethylene glycol dimercaptoacetate, dipentaerythritol hexa(3-mercaptopropionate), trimethylolpropane tri(3-mercaptopropionate), alkylmercaptoacetates, 3-mercaptopropyltrialkoxysilanes, and thiol-functional siloxane oligomers.

[0064] The molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K must be between 1:1 and 250:1. Preferably, it is between 1.5:1 and 150:1, particularly between 2:1 and 100:1, and most preferably between 2.5:1 and 75:1. This ratio allows the pot life to be adjusted within the intrinsic limits of the respective composition, determined, for example, by the catalyst content, the reactivity of the isocyanates, and their quantity. The lower limit of the pot life is the pot life obtained in a given composition using a specific amount of catalyst without the addition of compound T.In many cases suitable for the application close to the invention as a laminating adhesive, and due to the high amount of isocyanate groups in the presence of a catalyst but without compound T, no actual pot life is achieved, and the composition practically begins to harden upon mixing the two components. The upper limit of the adjustable pot life is therefore the pot life that would be achieved without the use of a catalyst due to the uncatalyzed isocyanate-hydroxyl reaction. This reaction also begins to start sometime after mixing the two components, even without the use of a catalyst. However, without a catalyst, the reaction proceeds much more slowly and results in the formation of inferior mechanical and other properties in the hardened material.

[0065] The key advantage achieved by the three-component polyurethane composition according to the invention is an exceptionally fast-curing and strength-building system that simultaneously exhibits a sufficiently long pot life for user-friendly processing. Furthermore, the required pressing time remains very short, even for composite materials, and is not susceptible to fluctuating humidity. This allows, for example, bonding to be carried out on larger substrates, which can then be further processed or transported very soon after the adhesive is applied and the substrates are briefly pressed. This leads, for instance, to a significant reduction in cycle times in industrial manufacturing. Another advantage of the polyurethane compositions according to the invention is the ability to adjust the pot life as described above.This is particularly advantageous for automated applications and can, for example, enable further optimization of cycle times in industrial manufacturing, as the pot life can be adjusted to the desired application.

[0066] To control this even more efficiently, it is advantageous if the first component A-1 and the second component A-2 contain not only different amounts of catalyst K, but also different amounts of compound T.

[0067] Accordingly, in preferred embodiments, the second component A-2 contains at least twice as much compound T as the first component A-1, based on the molar amount of thiol groups of compound T in the respective component.

[0068] In the same or other preferred embodiments of the three-component polyurethane composition according to the invention, the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K is higher in the second component A-2 than in the first component A-1.

[0069] In these embodiments, not only is there an absolutely higher amount of compound T in the second component A-2 than in the first component A-1, but also a higher amount relative to the respective amount of catalyst K. This allows the pot life of the composition to be adjusted even more precisely by mixing the two components A-1 and A-2.

[0070] In preferred embodiments, the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K in the second component A-2 is between 2.5:1 and 250:1, in particular between 5:1 and 100:1, and most preferably between 7.5:1 and 15:1.

[0071] In the same or other embodiments, the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K in the first component A-1 is between 1 :1 and 50:1, in particular between 1.1 :1 and 10:1, most preferably between 1.2:1 and 2.5:1.

[0072] The first component A-1 preferably contains 0.5 to 2.5 wt.%, preferably 0.75 to 1.5 wt.%, in particular 1.0 to 1.25 wt.%, compound T having at least one thiol group, based on the total of the first component A-1.

[0073] The second component A-2 preferably contains 1.0 to 5.0 wt.%, preferably 1.5 to 4.0 wt.%, in particular 2.0 to 3.0 wt.%, compound T having at least one thiol group, based on the total of the second component A-2.

[0074] The first component A-1 and the second component A-2 each contain at least one metal catalyst K for the reaction of hydroxyl groups and isocyanate groups, which can form thio complexes, wherein the first component A-1 contains at least 1.5 times the amount of metal catalyst K as the second component A-2, based on the molar amount of metal atoms of the metal catalyst K in the respective component.

[0075] Preferably, the first component A-1 contains at most 5 times the amount of metal catalyst K as the second component A-2, in order to obtain a well miscible composition and controllable pot life of the mixed composition.

[0076] Preferably, the composition according to the invention contains no further catalysts in catalytically effective amounts for the reaction of hydroxyl groups and isocyanate groups other than the described metal catalyst K, and in particular no organic catalysts such as amidines. Such additional catalysts would influence the curing reaction and thus disrupt the effect according to the invention.

[0077] Due to the different amounts of metal catalyst K in the first component A-1 and the second component A-2, the pot life of the mixed composition and the curing rate can be very precisely adjusted, solely by the mixing ratio of the two components A-1 and A-2.

[0078] Preferably, the first component A-1 contains 2 to 4 times the amount of metal catalyst K as the second component A-2, based on the molar amount of metal atoms of the metal catalyst K in the respective component, in particular 2.5 to 3 times the amount of metal catalyst K.

[0079] Therefore, all metal catalysts suitable as metal catalyst K are those which can be used as crosslinking catalysts in polyurethane chemistry and which can simultaneously form thio complexes with thiols in the presence of thiols.

[0080] Suitable metal catalysts K include, for example, bismuth, zinc, tin, iron or zirconium compounds, which includes complexes and salts of these metals.

[0081] Preferred materials include a bismuth(III), zinc(II), zirconium(IV), or tin(II) compound, or an organotin(IV) compound. Tin(IV), tin(II), and / or bismuth(III) compounds are most preferred because they possess particularly high activity while being the least sensitive to moisture.

[0082] The metal catalyst K particularly preferably comprises a bismuth compound, especially a bismuth(III) compound. A bismuth compound has the advantage of exhibiting low acute toxicity in addition to its desirable properties as a catalyst and thiocomplex former. A variety of conventional bismuth catalysts can be used as the bismuth compound. These include, for example, bismuth carboxylates such as bismuth acetate, oleate, octoate, or neodecanoate; bismuth nitrate; bismuth halides such as bromide, chloride, iodide, and bismuth sulfide; basic bismuth carboxylates such as bismutyl neodecanoate, bismuth subgallate, or bismuth subsalicylate; and mixtures thereof.

[0083] In a preferred embodiment, the metal catalyst K is a bismuth(III) complex comprising at least one 8-hydroxyquinoline-based ligand. Such complexes are described in EP 1551895. Preferably, this is a bismuth(III) carboxylate comprising one molar equivalent of an 8-hydroxyquinoline ligand.

[0084] In a further preferred embodiment, the metal catalyst K is a bismuth(III) complex comprising at least one ligand based on 1,3-ketoamide.

[0085] Such complexes are described in EP 2791153. Preferably, this is a bismuth(III) carboxylate having 1 to 3 molar equivalents of a 1,3-ketoamide ligand.

[0086] A variety of conventional tin catalysts can be used as tin compounds. Particularly suitable organotin compounds are dialkyltin oxides, dialkyltin dichlorides, dialkyltin dicarboxylates, and dialkyltin diketonates, especially dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin diacetylacetonate, dioctyltin oxide, dioctyltin dichloride, dioctyltin diacetate, dioctyltin dilaurate, or dioctyltin diacetylacetonate, or alkyltin thioesters.

[0087] In a preferred embodiment, the metal catalyst K is a doctyltin dicarboxylate, in particular dioctyltin dilaurate.

[0088] The first component A-1 preferably contains 0.5 to 2.5 wt.%, preferably 0.6 to 1.5 wt.%, in particular 0.7 to 1.2 wt.%, metal catalyst K, based on the total first component A-1.

[0089] The second component A-2 preferably contains 0.1 to 0.7 wt.%, more preferably 0.15 to 0.5 wt.%, and particularly 0.2 to 0.4 wt.%, metal catalyst K, based on the total amount of the second component A-2. Due to the high amount of metal catalyst K, especially in the first component A-1, exceptionally rapid curing after the end of the pot life can be achieved at any mixing ratio, which is highly desirable in industrial bonding processes, as it allows for increased cycle times.

[0090] The first component A-1 and the second component A-2 may contain further, optional components. These are listed in detail below.

[0091] A preferred first component A-1 contains, in each case with respect to the entire component A-1 ,

[0092] - 30 to 80 wt.%, preferably 40 to 70 wt.%, in particular 50 to 60 wt.%, polyol P,

[0093] - 1 to 25 wt.%, preferably 5 to 20 wt.%, in particular 10 to 15 wt.%, diol with two hydroxyl groups linked via a C2 to C9 carbon chain,

[0094] - 0.5 to 2.5 wt.%, preferably 0.75 to 2.0 wt.%, in particular 1.0 to 1.5 wt.%, compound T comprising at least one thiol group,

[0095] - 0.5 to 2.0 wt.%, preferably 0.6 to 1.5 wt.%, in particular 0.7 to 1.0 wt.%, metal catalyst K, and

[0096] - 10 to 50 wt.%, preferably 15 to 40 wt.%, in particular 20 to 30 wt.%, fillers, and optionally other components.

[0097] A preferred second component A-2 contains, in each case with respect to the entire component A-2,

[0098] - 30 to 80 wt.%, preferably 40 to 70 wt.%, in particular 50 to 60 wt.%, polyol P,

[0099] - 1 to 25 wt.%, preferably 5 to 20 wt.%, in particular 10 to 15 wt.%, diol with two hydroxyl groups linked via a C2 to C9 carbon chain,

[0100] - 1.0 to 3.5 wt.%, preferably 1.5 to 3.0 wt.%, in particular 2.0 to 2.5 wt.%, compound T comprising at least one thiol group,

[0101] - 0.1 to 2.0 wt.%, preferably 0.15 to 1.0 wt.%, in particular 0.2 to 0.5 wt.%, metal catalyst K, and

[0102] - 10 to 50 wt.%, preferably 15 to 40 wt.%, in particular 20 to 30 wt.%, fillers, and optionally other components.

[0103] The third component B

[0104] The third component B initially contains at least one polyisocyanate I.

[0105] The polyisocyanate I is present in relatively high quantities, which is very advantageous for developing sufficiently good mechanical properties for use as a laminating adhesive.

[0106] The third component preferably contains enough polyisocyanate I to contain at least 2.5 wt.%, in particular at least 3 wt.%, preferably at least 5 wt.%, based on the total polyurethane composition, isocyanate groups.

[0107] Any commercially available polyisocyanates suitable for polyurethane production, especially diisocyanates, can be used as polyisocyanate I.

[0108] Suitable polyisocyanates are in particular monomeric di- or triisocyanates, as well as oligomers, polymers and derivatives of the monomeric di- or triisocyanates, and any mixtures thereof.

[0109] Suitable aromatic monomeric di- or triisocyanates include, in particular, 2,4- and 2,6-toluene diisocyanate and any mixtures of these isomers (TDI), 4,4'-, 2,4'- and 2,2'-diphenylmethane diisocyanate and any mixtures of these isomers (MDI), mixtures of MDI and MDI homologs (polymeric MDI or PMDI), 1,3- and 1,4-phenylene diisocyanate, 2,3,5,6-tetramethyl-1,4-diisocyanatobenzene, naphthalene-1,5-diisocyanate (NDI), 3,3'-dimethyl-4,4'-diisocyanatodiphenyl (TODI), dianisidine diisocyanate (DADI), 1,3,5-tris-(isocyanatomethyl)benzene, tris-(4-isocyanatophenyl)methane and tris-(4-isocyanatophenyl)thiophosphate.

[0110] Suitable aliphatic monomeric di- or triisocyanates are in particular 1,4-

[0111] Tetramethylene diisocyanate, 2-methylpentamethylene-1,5-diisocyanate, 1,5-

[0112] Pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), 2,2,4- and 2,4,4-trimethyl-1,6-hexamethylene diisocyanate (TMDI), 1,10-decamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, lysine and lysine ester diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-methyl-2,4- and -2,6-diisocyanatocyclohexane and any mixtures of these isomers (HTDI or HeTDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (=isophorone diisocyanate or IPDI), perhydro-2,4'- and -4,4'-diphenylmethane diisocyanate (HMDI or H12MDI), 1,4-diisocyanato-2,2,6- trimethylcyclohexane (TMCDI), 1,3- and 1,4-bis-(isocyanatomethyl)cyclohexane, m- and p-xylylene diisocyanate (m- and p-XDI), m- and p-tetramethyl-1,3- and -1,4-xylylene diisocyanate (m- and p-TMXDI), bis-(1-isocyanato-1-methylethyl)naphthalene, dimer and trimer fatty acid isocyanates such as 3,6-bis-(9-isocyanatononyl)-4,5-di-(1-heptenyl)cyclohexene (dimeryl diisocyanate) and α,α,α',α',α",α"-hexamethyl-1,3,5-mesitylene triisocyanate.

[0113] The preferred technologies are MDI, TDI, HDI and IPDI.

[0114] Suitable oligomers, polymers and derivatives of the aforementioned monomeric di- and triisocyanates are in particular derived from MDI, TDI, HDI and IPDI.Particularly suitable are commercially available types, especially HDI biuretes such as Desmodur® N 100 and N 3200 (from Covestro), Tolonate® HDB and HDB-LV (from Vencorex) and Duranate® 24A-100 (from Asahi Kasei); HDI isocyanurates, such as Desmodur® N 3300, N 3600 and N 3790 BA (all from Covestro), Tolonate® HDT, HDT-LV and HDT-LV2 (from Vencorex), Duranate® TPA-100 and THA-100 (from Asahi Kasei) and Coronate® HX (from Nippon Polyurethane); HDI uretdiones such as Desmodur® N 3400 (from Covestro); HDI iminooxadiazindiones such as Desmodur® XP 2410 (from Covestro); HDI allophanes such as Desmodur® VP LS 2102 (from Covestro); IPDI isocyanurates, such as in solution as Desmodur® Z 4470 (from Covestro) or in solid form as Vestanat® T1890 / 100 (from Evonik); TDI oligomers such as Desmodur® IL (from Covestro); and mixed isocyanurates based on TDI / HDI, for example as Desmodur® HL (from Covestro).Also particularly suitable are liquid forms of MDI at room temperature (so-called "modified MDI"), which are mixtures of MDI with MDI derivatives, such as MDI carbodiimides, MDI uretonides, or MDI urethanes, known under trade names such as Desmodur® CD, Desmodur® PF, Desmodur® PC (all from Covestro) or Isonate® M 143 (from Dow), as well as mixtures of MDI and MDI homologs (polymeric MDI or PMDI), available under trade names such as Desmodur® VL, Desmodur® VL50, Desmodur® VL R10, Desmodur® VL R20, Desmodur® VH 20 N and Desmodur® VKS 20F (all from Covestro), Suprasec® 2030 and Suprasec® 2050 (from Huntsman), Isonate® M 309, Voranate® M 229 and Voranate® M 580 (both from Dow) or Lupranat® M 10 R (from BASF). In practice, the aforementioned oligomeric polyisocyanates typically represent mixtures of substances with different degrees of oligomerization and / or chemical structures. Preferably, they exhibit an average NCO functionality of 2.1 to 4.0.

[0115] Preferably, the polyisocyanate I is selected from the group consisting of MDI, TDI, HDI and IPDI and oligomers, polymers and derivatives of the aforementioned isocyanates, as well as mixtures thereof.

[0116] Preferably, the polyisocyanate contains isocyanurate, iminooxadiazin ione, uretdione, biuret, allophane, carbodiimide, uretonimine or oxadiazintrione groups.

[0117] Particularly preferred as polyisocyanates are liquid forms of MDI at room temperature. These are especially so-called polymeric MDI as well as MDI with proportions of oligomers or derivatives thereof. The MDI content (=4,4'-, 2,4'- or 2,2'-diphenylmethane diisocyanate and any mixtures of these isomers) of such liquid forms of MDI is particularly 50 to 95 wt.%, and more specifically 60 to 90 wt.%.

[0118] Particularly preferred as a polyisocyanate is polymeric MDI and MDI types that are liquid at room temperature and contain proportions of MDI carbodiimides or their adducts.

[0119] These polyisocyanates provide particularly good processing properties and especially high strengths.

[0120] The polyisocyanate I of the third component B may contain proportions of isocyanate-containing polyurethane polymers. Either the second component may comprise a separately produced isocyanate-containing polyurethane polymer, or the polyisocyanate may have been mixed with at least one polyol, for example a polyol P as described above, in particular a polyether polyol, wherein the isocyanate groups are present in a stoichiometric excess relative to the OH groups.

[0121] The mechanical properties of the composition can be improved by using polyurethane polymers containing isocyanate groups. Therefore, they are included in preferred embodiments. Component B preferably contains 50 to 100 wt.%, in particular 60 to 75 wt.%, polyisocyanate I, based on the third component B.

[0122] In preferred embodiments, component B comprises between 45 and 70 wt.%, in particular between 50 and 60 wt.%, polyisocyanate I, which is not a polyurethane polymer, in particular polymeric MDI and / or MDI types that are liquid at room temperature and contain proportions of MDI carbodiimides or their adducts, as well as up to 20 wt.%, in particular between 5 and 15 wt.%, isocyanate group-containing polyurethane polymer.

[0123] In preferred embodiments, the composition according to the invention contains at least one drying agent. It is preferred that at least the third component B contains at least one drying agent, preferably also at least one of components A-1 and A-2.

[0124] A desiccant increases storage stability and is particularly advantageous for large-area lamination applications.

[0125] All chemical or physical drying agents commonly used in polyurethane chemistry are suitable as drying agents.

[0126] Suitable materials include reactive silanes such as tetraethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane or organoalkoxysilanes, which have a functional group in the α-position to the silane group, in particular N-(methyldimethoxysilylmethyl)-O-methylcarbamate, (methacryloxymethyl)silanes, methoxymethylsilanes, oligomeric forms of these silanes, molecular sieve powders, calcium oxide, highly reactive isocyanates such as p-tosyl isocyanate, monomeric diisocyanates, mono-oxazolidines such as Incozol® 2 (from Incorez) or orthoformic acid esters.

[0127] Molecular sieves or zeolites based on aluminosilicate, especially in fine powder form, as well as moisture-reactive organosilanes or -siloxanes are preferred as drying agents.

[0128] Component B preferably contains 1 to 20 wt.%, preferably 2 to 15 wt.%, in particular 3 to 10 wt.%, desiccant, based on the third component B. Components A-1 and A-2 contain, independently of each other, preferably 0.5 to 10 wt.%, preferably 1 to 7.5 wt.%, in particular 2 to 5 wt.%, desiccant, based on the respective component A-1 or A-2.

[0129] Drying agents are particularly preferred when the substrates to be bonded are very moist.

[0130] A preferred third component B contains, in each case with respect to the entire component B,

[0131] - 30 to 80 wt.%, preferably 40 to 70 wt.%, in particular 50 to 60 wt.%, polyisocyanate I, which is not a polyurethane polymer,

[0132] - 1 to 25 wt.%, preferably 5 to 20 wt.%, in particular 7.5 to 15 wt.%, isocyanate group-containing polyurethane polymer,

[0133] - 1 to 15 wt.%, preferably 2 to 12 wt.%, in particular 3 to 10 wt.%, drying agent,

[0134] - 0.5 to 15 wt.%, preferably 1 to 10 wt.%, in particular 2.5 to 7.5 wt.% plasticizers, and

[0135] - 5 to 50 wt.%, preferably 10 to 40 wt.%, in particular 20 to 30 wt.%, fillers, and optionally other components.

[0136] Other components

[0137] The polyurethane composition according to the invention can contain, in some or all components, in addition to the necessary components already mentioned, further optional components, such as those known to those skilled in the art from multi-component polyurethane chemistry. These can be present in only one component, in two components, or in all components in the same or different amounts.

[0138] Further preferred components include inorganic and organic fillers, such as, in particular, natural, ground or precipitated calcium carbonates, which may optionally be coated with fatty acids, especially stearic acid, barite (barytes), talcs, quartz flours, quartz sand, dolomites, wollastonites, kaolins, calcined kaolins, mica (potassium aluminum silicate), aluminum oxides, aluminum hydroxides, magnesium hydroxide, silicas including highly dispersed silicas from pyrolysis processes, industrially produced carbon black, graphite, metal powders such as aluminum, copper, iron, silver or steel, PVC powders or hollow spheres, as well as flame-retardant fillers such as hydroxides or hydrates, in particular hydroxides or hydrates of aluminum, preferably aluminum hydroxide.

[0139] The addition of fillers is advantageous in that it increases the strength of the cured polyurethane composition.

[0140] Preferably, the polyurethane composition contains at least one filler selected from the group consisting of calcium carbonate, carbon black, kaolin, fumed silica, barite, talc, quartz flour, dolomite, wollastonite, kaolin, calcined kaolin, and mica. Ground calcium carbonate, calcined kaolin, and fumed silica are particularly preferred fillers. The latter also has a thickening effect and can increase thixotropy.

[0141] It can be advantageous to use a mixture of different fillers. Combinations of calcined kaolin and pyrogenic silica are most preferred.

[0142] In preferred embodiments of the polyurethane composition according to the invention, at least one of the three components A-1 , A-2 and B additionally contains at least one filler, preferably both components A-1 and A-2 and particularly preferably all three components.

[0143] Preferably, this consists of calcined kaolin and pyrogenic silica. The use of fillers has the advantage that not only can the composition be formulated more cost-effectively, but the mechanical properties, application characteristics such as viscosity and thixotropy, and other properties such as electrical conductivity, thermal conductivity, or flammability can also be positively influenced.

[0144] Further components may include, in particular, solvents, plasticizers and / or extenders, pigments, rheology modifiers such as polyamide waxes and urea compounds, adhesion promoters such as organofunctional trialkoxysilanes, stabilizers against oxidation, heat, light and UV radiation, flame retardants, and surfactants, especially wetting agents and defoamers. All substances commonly used in polyurethane chemistry within the respective class are suitable for these additives. A preferred three-component polyurethane composition consists of a first component A-1, which, based on the total component A-1,

[0145] - 30 to 80 wt.%, preferably 40 to 70 wt.%, in particular 50 to 60 wt.%, polyol P,

[0146] - 1 to 25 wt.%, preferably 5 to 20 wt.%, in particular 10 to 15 wt.%, diol with two hydroxyl groups linked via a C2 to C9 carbon chain,

[0147] - 0.5 to 2.5 wt.%, preferably 0.75 to 2.0 wt.%, in particular 1.0 to 1.5 wt.%, compound T comprising at least one thiol group,

[0148] - 0.5 to 2.0 wt.%, preferably 0.6 to 1.5 wt.%, in particular 0.7 to 1.0 wt.%, metal catalyst K,

[0149] - 10 to 50 wt.%, preferably 15 to 40 wt.%, in particular 20 to 30 wt.%, fillers, and optionally further components; and a second component A-2, which, in each case based on the total component A-2,

[0150] - 30 to 80 wt.%, preferably 40 to 70 wt.%, in particular 50 to 60 wt.%, polyol P,

[0151] - 1 to 25 wt.%, preferably 5 to 20 wt.%, in particular 10 to 15 wt.%, diol with two hydroxyl groups linked via a C2 to C9 carbon chain,

[0152] - 1.0 to 3.5 wt.%, preferably 1.5 to 3.0 wt.%, in particular 2.0 to 2.5 wt.%, compound T comprising at least one thiol group,

[0153] - 0.1 to 2.0 wt.%, preferably 0.15 to 1.0 wt.%, in particular 0.2 to 0.5 wt.%, metal catalyst K, and

[0154] - 10 to 50 wt.%, preferably 15 to 40 wt.%, in particular 20 to 30 wt.%, fillers, and optionally further components; and a third component B, which, in relation to the entire component B,

[0155] - 30 to 80 wt.%, preferably 40 to 70 wt.%, in particular 50 to 60 wt.%, polyisocyanate I, which is not a polyurethane polymer, - 1 to 25 wt.%, preferably 5 to 20 wt.%, in particular 7.5 to 15 wt.%, isocyanate group-containing polyurethane polymer,

[0156] - 1 to 15 wt.%, preferably 2 to 12 wt.%, in particular 3 to 10 wt.%, drying agent,

[0157] - 0.5 to 15 wt.%, preferably 1 to 10 wt.%, in particular 2.5 to 7.5 wt.% plasticizers, and

[0158] - Contains 5 to 50 wt.%, preferably 10 to 40 wt.%, in particular 20 to 30 wt.%, fillers, and optionally other components.

[0159] The first component A-1, the second component A-2, and the third component B are preferably formulated such that their mixing ratio in parts by volume is in the range of (A-1 + A-2) : B = 1 : 1, as is the case in the preferred embodiments described above. Such a mixing ratio is particularly easy to control and leads to a particularly homogeneous mixture. The respective combination of component A-1 and component A-2 should preferably have the same volume as component B. Other mixing ratios can also be used, for example (A-1 + A-2) : B = 10 : 1, as long as the resulting NCO:OH ratio in the mixture of all components is within the correct range.

[0160] The mixing ratio of A-1 and A-2 can be varied as desired, as long as the total quantity of the mixture remains constant. It is possible to mix only the first component, A-1, with the third component, B, resulting in a particularly short pot life. Likewise, it is possible to mix only the second component, A-2, with the third component, B, resulting in a particularly long pot life. However, by adjusting the mixing ratio of the first component, A-1, and the second component, A-2, any desired pot life within this range can be set gradually and very precisely.

[0161] The present invention therefore makes it possible to dynamically adjust the pot life continuously throughout the bonding process, solely by changing the mixing ratio of components A-1 and A-2. This enables multilayer bonding, allowing for an individual pot life for each adhesive layer, which drastically increases the efficiency of the entire process. In the mixed polyurethane composition, the ratio between the number of isocyanate groups and the number of isocyanate-reactive groups (NCO:OH ratio) before curing is preferably in the range of approximately 1.2 to 1, more preferably 1.15 to 1.05. However, it is also possible, although usually not preferred, for a substoichiometric proportion of isocyanate groups compared to isocyanate-reactive groups to be present.

[0162] The three components are manufactured separately and preferably in the absence of moisture. Each of the three individual components is typically stored in its own container. The additional, optional components of the polyurethane composition can be present as part of the first, second, and / or third component, with any additional components reactive towards isocyanate groups preferably being part of the first or second component. Suitable containers for storing each component include, in particular, a drum, pail, bag, bucket, can, cartridge, or tube. All components are individually stable, meaning they can be stored for several months up to a year or longer before use without any significant change in their respective properties relevant to their application.

[0163] The three components are stored separately before the composition is mixed and only mixed together during or immediately before application.

[0164] The mixing order is not restricted. It is possible to mix the components in any order, or to create a premix from two of the three components, to which the remaining component is then added. It is also possible to achieve a mixture by simultaneously adding all three components at once, for example, to a static or dynamic mixer. The individual components can be introduced at the same point in the mixer, or at different points, so that a premix of two components (for example, A-1 and A-2) takes place before the remaining component (for example, component B) is added.

[0165] Mixing is typically carried out using static or dynamic mixers. During mixing, care must be taken to ensure that the three components are mixed as homogeneously as possible. If the three components are not mixed completely, local deviations from the advantageous mixing ratio will occur, which can result in a deterioration of the mechanical or other properties.

[0166] Upon contact of the first two components, A-1 and A-2, with the third component, B, curing begins after the pot life has elapsed, through a chemical reaction. In this process, the hydroxyl groups and any other substances reactive towards isocyanate groups react with the isocyanate groups. Excess isocyanate groups react primarily with moisture. As a result of these reactions, the polyurethane composition cures into a solid material. This process is also known as cross-linking.

[0167] The described three-component polyurethane composition is advantageously usable as a laminating adhesive, in particular for the production of composite elements, especially multi-layer wood panels, or for the production of sandwich panels, for example for facade construction.

[0168] A further object of the invention is a method for bonding at least three substrates layer by layer, comprising the steps in the following order: a) providing the first component A-1, the second component A-2, and the third component B as described above, wherein each of the three components is connected to a mixing chamber via its own pump and can be conveyed separately; b) conveying the required quantity of the first component A-1, the second component A-2, and the third component B to the mixing chamber and mixing the components by means of a static or dynamic mixer, wherein the mixing ratio of components A-1, A-2, and B is controlled via the delivery rate of the respective pump and is set before the mixing process and optionally corrected during the mixing process; c) applying the mixed polyurethane composition from the mixing chamber to the surface of one of the substrates to be bonded;d) Adding another substrate onto the applied adhesive; e) Repeating steps b) to d) until all substrates are joined layer by layer using adhesive, with each subsequent bonding operation using a higher proportion of the first components A-1 and a lower proportion of the second components A-2 than in the previous bonding operation; e) optionally, pressing the joined substrates together within the pot life of all applied adhesive layers until the adhesive layers have cured sufficiently to allow the bonded substrates to be moved.

[0169] The two substrates can be made of the same or different materials.

[0170] In these bonding processes, suitable substrates are particularly important

[0171] - Glass, glass ceramics, glass mineral fiber mats;

[0172] - Metals and alloys, such as aluminium, iron, steel and non-ferrous metals, as well as surface-treated metals and alloys, such as galvanised or chromium-plated metals;

[0173] - coated and painted substrates, such as powder-coated metals or alloys and painted sheets;

[0174] - Plastics such as polyvinyl chloride (rigid and flexible PVC), acrylonitrile butadiene styrene copolymers (ABS), polycarbonate (PC), polyamide (PA), poly(methyl methacrylate) (PMMA), polyesters, epoxy resins, in particular epoxy-based thermosets, polyurethanes (PUR), polyoxymethylene (POM), polyolefins (PO), polyethylene (PE) or polypropylene (PP), ethylene / propylene copolymers (EPM) and ethylene / propylene / diene terpolymers (EPDM), wherein the plastics may preferably be surface-treated by plasma, corona or flame;

[0175] - Fiber-reinforced plastics, such as carbon fiber reinforced plastics (CFRP), glass fiber reinforced plastics (GFRP) and sheet moulding compounds (SMC);

[0176] - Foams, mineral wool mats, textiles or other insulating materials;

[0177] - Wood, especially softwood, beechwood, oakwood, maplewood or other woods;

[0178] - Wood treated with resins, for example phenolic, melamine or epoxy resins, bonded wood-based materials, resin-textile composites and other so-called polymer composites; as well as

[0179] - Concrete, mortar, bricks, plaster and natural stones such as granite, limestone and sandstone or marble.

[0180] Preferred substrates are wood panels, and the process is preferably a process for producing multilayer wood panels, particularly three-layer panels. The substrates can be pretreated, if necessary, before applying the composition. Such pretreatments include, in particular, physical and / or chemical cleaning processes, as well as the application of an adhesion promoter, an adhesion promoter solution, an activator, or a primer. In the case of wood substrates, this can also include sanding, roughening, drying, staining, or other wood treatments.

[0181] Preferably, the composition according to the invention is applied in mixed form over the entire surface or as beads to a substrate surface, particularly with a layer thickness of between 100 pm and 2.5 mm, preferably with a thickness of 1 to 5 mm, and more preferably 2 to 3 mm, in the case of beads. The beads are pressed together at the end of the process to form a thin, continuous adhesive layer.

[0182] The application is normally carried out via several nozzles arranged in parallel, for example 5 to 30 nozzles, depending on the substrate area.

[0183] In preferred embodiments of the inventive method, the application of the mixed polyurethane composition is carried out fully automatically using a robot or 3D printer. Using this technique, the application nozzles are guided over the substrate surface, and the mixed composition is applied by moving a movable arm or axis equipped with the application nozzles over the substrate surface. The amount of adhesive dispensed is determined by the speed of the nozzle arm or axis and the pumping speed of the mixed composition through the nozzles.

[0184] Depending on the system, the output quantity can range from a few hundred grams to a few thousand grams of adhesive per minute.

[0185] Furthermore, it is preferably possible to control whether the order is carried out with a smaller quantity over 2 trips (order slightly offset on the outward and return journey) or with a larger quantity in 1 trip of the application arm.

[0186] Preferably, the dosing system continuously measures the actual application quantity via pressure measurements before and after the dosing pump. Preferably, the rotational speeds of the pumps for feeding components A-1, A-2, and B into the mixing chamber and the rotational speed of the pump(s) for conveying the mixed composition to the dosing system are continuously measured and stored or at least displayed. In preferred embodiments, this allows the control computer to detect and compensate for errors, and a warning can be issued if the pump speed becomes too low. The minimum value of typical pump speeds is approximately 10 revolutions per minute (rpm), while the maximum value can be, for example, up to 150 rpm.

[0187] A suitable system or arrangement for carrying out the method according to the invention comprises separate material containers for components A-1, A-2 and B, a separate pump for each component, wherein the pumps are arranged to pump the components of the adhesive composition to be produced through the outlet lines to the mixing unit, a movable arm or axis on which the application nozzles are arranged and a control unit of the system, wherein the control unit: determines the mixing ratio of the adhesive components, in particular components A-1 and A-2, for each adhesive layer;The control unit controls the individual pumps and their respective delivery rates to pump the adhesive components to the mixing unit in a mixing ratio determined by the control unit, the control unit being configured to control the ratio of components A-1 and A-2 of the adhesive to be applied to a substrate during application in such a way that the pot life of the applied adhesive in each subsequently applied adhesive layer is reduced compared to the previous one; controls the movement of the application arm and the application speed of the mixed polyurethane composition.

[0188] A suitable such system is disclosed, for example, in WO 2018 / 134476 A1, in particular on p. 6, line 8 to p. 8, line 24 and figure 2.

[0189] Preferably, the inventive method is controlled by a control unit comprising a computer that monitors and controls all aspects of the method, in particular at least the pump speeds of the individual components and of the mixed adhesive, as well as the application speed of the adhesive onto the substrate. The control unit can be designed to display certain parameters, such as the pump speed, on a connected screen or to send them to display devices, so that a user can monitor them and, if necessary, influence them via a control system.

[0190] The control unit can also be designed so that a computer fully automatically monitors and controls these processes, so that no user interaction is absolutely necessary during the gluing process.

[0191] In preferred embodiments of the method, in which a computer at least partially controls the process parameters, in particular the speed of the pumps and the movement of the application device, for example the arm or the axis with the nozzles, a computer program or electronically stored algorithm is required to program the computer accordingly.

[0192] A corresponding computer program preferably includes corresponding computer codes which calculate the mutual mixing ratio of components A-1, A-2 and B at the time of the start of the process for each adhesive layer and program the control unit of the system accordingly so that the process is carried out accordingly.

[0193] The optimal starting mixture ratio of the various components, in particular components A-1 and A-2, can be determined and set via the control unit of the system, which preferably comprises a computer, at the start time of the adhesive application, preferably depending on the current ambient temperature and / or the temperature of components A-1, A-2 and / or B and / or the temperature of the mixed adhesive composition and / or the temperature of the production area used for bonding the substrates and / or the temperature of the substrates themselves.

[0194] Furthermore, to determine the mixing ratio of components A-1 and A-2 at the beginning and during the process, the reaction rate curves measured experimentally, particularly at different temperatures, as described below in the experimental section of this document, can preferably be used to calculate the mixing ratio of the various components. This data is preferably stored in a database and accessible to the user or the computer program.

[0195] This calculation can be performed before the start of the process, for example by programming the control unit by a user or a computer program, or recalculated during the process itself if errors are detected or parameter fluctuations, such as temperature fluctuations, are measured.

[0196] In the progressive process, the control unit preferably continuously and steplessly controls the preferably known reaction rate profile based on the mixing ratio of the various components of the adhesive to be produced, such that towards the end of the process the proportion of component A-1 in the adhesive mixture is increased.

[0197] In all cases, the supply of the two components A-1 and A-2 must be controlled so that the total amount of these two components in the adhesive mixture remains constant, ensuring that the NCO:OH ratio, determined by the ratio of the sum of components A-1 and A-2 to component B, always remains the same. For example, at the beginning of the process, an adhesive mixture with 90% component A-2, 10% component A-1, and 100% component B can be used for the first adhesive layer, and for the second adhesive layer, an adhesive mixture with 50% component A-2, 50% component A-1, and 100% component B.

[0198] The system is preferably equipped with several temperature sensors. These sensors measure the current ambient temperature and / or the temperature of components A-1, A-2 and / or B and / or the mixed adhesive composition and / or the temperature of the production area used for bonding the substrates and / or the temperature of the substrates themselves.

[0199] The system is preferably equipped with additional sensors in the same or other embodiments, for example humidity sensors that measure, for example, the humidity or substrate moisture, as well as pressure and / or flow sensors that monitor the performance of the pumps.

[0200] All data collected in this way can be displayed as parameters on monitors or control displays, or fed directly into a computer of the control unit. This allows for manual or automatic corrective intervention in the process if necessary, should one or more of these parameters influence the set pot life. Correction includes, in particular, the dynamic adjustment of the mixing ratio of components A-1 and A-2.

[0201] In a particularly preferred embodiment of the inventive method, the mixing ratio of components A-1, A-2 and B is calculated in advance for each adhesive layer, taking into account the ambient temperature during the execution of the method when calculating the mixing ratio.

[0202] In the same or other particularly preferred embodiments of the inventive method, the mixing ratio of components A-1, A-2, and B for each adhesive layer is calculated by a computer during the process and adjusted as needed, wherein parameters are measured by at least one sensor during the process, which are read into the computer and which influence the calculation of the mixing ratio. In particular, these parameters are selected from ambient temperature, humidity, temperature of components A-1, A-2, and / or B or of the mixed composition, substrate temperature, and substrate moisture.

[0203] At the end of the inventive process, when all substrates have been bonded layer by layer with the adhesive layers, the resulting article is preferably pressed. Pressing firmly bonds the still-cured adhesive to the substrates and increases the stability of the bonded article. Pressing is not always necessary, for example, with substrates that are heavy, but it is preferred, especially with substrates that have porous and not perfectly flat surfaces, such as wood.

[0204] It is important that the compression of the joined substrates begins within the pot life of all applied adhesive layers.

[0205] The pressing process should last significantly longer than the pot life of the last applied adhesive at the end of the final layer application to ensure sufficient curing during pressing. Preferably, the pressing time should be twice as long as the pot life of the last applied adhesive in the final adhesive layer. This ensures sufficient curing in all cases.

[0206] The described bonding process results in an article in which the cured adhesive composition bonds at least three substrates together via at least two adhesive layers.

[0207] This article is in particular a sandwich element of a lightweight structure, an industrial good or a consumer good, in particular a composite panel, a sandwich element or a multi-layer element which can be used for buildings or industrial manufacturing, in particular insulation panels for facade construction and most preferably laminated wood panels, in particular three-layer panels.

[0208] Another aspect of the invention is the use of a three-component polyurethane composition as described above as a laminating adhesive for bonding at least three substrates.

[0209] Preferred use is for the manufacture of composite panels and sandwich elements, in particular insulation panels for facade construction and especially laminated wood panels, in particular three-layer panels.

[0210] Examples

[0211] Substances used:

[0212] Table 1 below lists the substances used in the example compositions. The raw materials were used as purchased, without further treatment.

[0213]

[0214] Table 1: Substances used

[0215] Synthesis of Prepolymer 1

[0216] 1,300 g of polyoxypropylene diol (Acclaim® 4200, from Covestro AG; OH number 28 mg KOH / g), 2,600 g of ethylene oxide-terminated polyoxypropylene triol (Voranol® CP 4755, from DowDuPont Inc.; OH number 35 mg KOH / g), 600 g of 4,4'-diphenylmethane diisocyanate (Desmodur® 44 MC L, from Covestro AG), and 500 g of diisodecyl phthalate were reacted at 80 °C according to a known process to form an NCO-terminated polymer that is liquid at room temperature and has an isocyanate group content of 2.05 wt%. Preparation of components of the polyurethane composition.

[0217] For each component composition, the ingredients listed in Tables 2 to 4, in the specified quantities (in parts by weight or wt%), of the first component A-1 (Table 2) were processed into a homogeneous paste using a vacuum dissolver under exclusion of moisture and stored in an airtight container. Similarly, the ingredients listed in Tables 3 and 4 for the second component A-2 (Table 3) and the third component B (Table 4) were processed and stored.

[0218] Table 2: Composition of Component A-1

[0219] Table 3: Composition of Component A-2

[0220] Table 4: Composition of Component B

[0221] Measuring pot times

[0222] The pot life of a series of three-component polyurethane compositions according to the invention was measured at various temperatures. In all examples, a 1:1 mixture (by volume) of component A (component A-1 plus component A-2 premixed) to component B was used.

[0223] The pot life was measured with a rheometer as the time until the complex viscosity after mixing the two components reached 1000 Pa s. The complex viscosity was measured on a thermostatically controlled plate-plate rheometer MCR 302 (Anton Paar) with a plate diameter of 25 mm and a plate spacing of 1 mm at an angular frequency of 6 rad s. -1(0.95 Hz) and a defined temperature (15°C, 20°C, or 30°C, each at 50% relative humidity). The deformation was 0.2%. The compositions to be measured were inserted into a dual-cartridge gun, with one cartridge containing component B and the other component A (component A-1 or component A-2, or the mixtures thereof defined in the respective test). The respective components were pre-tempered in their respective cartridges for 24 hours at the respective measurement temperature. The mixture to be measured was dispensed from the gun via an attached static mixer and applied directly to the rheometer plate, and the viscosity measurement was performed immediately after application. Figure 1 shows the measurement of test V-4 (see Table 5) with 50% component A-1 and 50% component A-2 (by volume) at 20°C.It is clearly evident that the complex viscosity remains consistently very low for a long time, but suddenly begins to rise rapidly at 4.3 minutes. This time (defined by reaching 1000 Pa s) marks the end of the pot life and the beginning of the very rapid curing reaction.

[0224] Table 5 below shows experiments V-1 to V-5, which represent pot life measurements with different volumetric proportions of component A-1 and component A-2 at various temperatures. The mixing ratio of component A (either pure component A-1 or A-2, or the specified mixture thereof) to component B was always 1:1 (volumetric).

[0225] Table 5: Measurement of the pot lives of various compositions according to the invention (experiments V-1 to V-5)

[0226] For industrial multi-layer bonding processes, pot lives between 1.5 and 9 minutes are ideal, with the longest pot life set for the first adhesive layer and the shortest for the last. For example, when bonding three substrate layers with two adhesive layers, it is recommended for efficiency reasons that the second adhesive layer has approximately half the pot life of the first.

[0227] The data from Table 5 show that, at any typical temperature in a production hall, an ideal pot life for each adhesive layer can be set solely by adjusting the ratio of components A-1 and A-2. This can even be adjusted during the process should a significant temperature fluctuation occur. Methods for bonding substrates

[0228] The following describes the implementation of a process according to the invention on a commercially available three-component system for bonding three-layer wood panels.

[0229] The bonding was carried out at 20°C.

[0230] Softwood boards were used as substrates, with substrates 1 to 3 being identical in the experiment.

[0231] The adhesives used in the first gluing step were composition V-4 (see Table 5) and in the second gluing step were composition V-2 (see Table 5).

[0232] The individual steps of the process are shown in Table 6, including the time required for each step and the total time elapsed after each step. It is important that the pot life of all adhesive layers has not yet expired at the start of the pressing process. The respective pot life begins immediately after mixing (at the start of the application) of the respective adhesive, i.e., after 0.9 minutes for adhesive layer 1 and after 2.4 minutes for adhesive layer 2.

[0233] Pot life (20°C) = 4.3 min; ** Pot life (20°C) = 1.9 min

[0234] The pressing process should last at least as long as the pot life of each adhesive compound, plus any remaining pot life of the applied adhesive layers. In this case, the pressing time was calculated as the pot life of the first applied adhesive layer at the end of the layer application, plus the remaining pot life of that adhesive compound, ensuring a sufficiently strong bond.

[0235] For comparison, a non-inventive method was carried out which had the same mixing ratio in component A (i.e., the mixture of A-1 and A-2) for both adhesive layers. This simulates a prior art two-component polyurethane composition, or a method as disclosed in WO 2023 / 031304 A1.

[0236] This process was carried out on the same equipment with the same substrates at the same temperature. The process steps are shown in Table 7.

[0237] Table 7: Non-inventive method using an adhesive (V-4) at 20°C. * Pot life

[0238] (20°C) = 4.3 min

[0239] The data from Tables 6 and 7 show that the inventive process enables much longer cycle times. Furthermore, it allows the process to respond to changing conditions, such as changing temperatures. In such cases, the desired pot life can be easily adjusted by dynamically changing the ratio of A-1 and A-2. The NCO:OH ratio in the composition remains constant, ensuring complete curing.

Claims

Patent claims 1. Three-component polyurethane composition suitable as a laminating adhesive, consisting of three components A-1, A-2 and B which are to be mixed during application; wherein - the first component A-1 and the second component A-2 each - at least one polyol P with an OH functionality in the range of 1.5 to 4 and a number-mean molecular weight M n in the range of 250 to 15,000 g / mol, as well as - at least one metal catalyst K for the reaction of hydroxyl groups and isocyanate groups, which can form thio complexes, as well as - comprising at least one compound T comprising at least one thiol group; wherein the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K in the first component A-1 and in the second component A-2 is between 1:1 and 250:1 respectively; and - the third component B - comprising at least one polyisocyanate I; characterized in that the first component A-1 contains at least 1.5 times the amount of metal catalyst K as is contained in the second component A-2, based on the molar amount of metal atoms of the metal catalyst K in the respective component.

2. Three-component polyurethane composition according to claim 1, characterized in that the metal catalyst K comprises a tin(IV) compound, a tin(II) compound, and / or a bismuth(III) compound.

3. Three-component polyurethane composition according to claim 1 or 2, characterized in that the molar ratio of all thiol groups of the at least one compound T to all metal atoms of the at least one metal catalyst K in the second component A-2 is higher than in the first component A-1.

4. Three-component polyurethane composition according to one of the preceding claims, characterized in that the at least one compound T comprises a polythiol compound with 1 to 6 thiol groups or a mixture of such compounds.

5. Three-component polyurethane composition according to claim 4, characterized in that the at least one compound T is selected from the group consisting of ethylene glycol di(3-mercaptopropionate), ethylene glycol dimercaptoacetate, dipentaerythritol hexa(3-mercaptopropionate), Trimethylolpropane tri(3-mercaptopropionate), alkylmercaptoacetates, 3-mercaptopropyltrialkoxysilanes, and thiol-functional siloxane oligomers.

6. Three-component polyurethane composition according to one of the preceding claims, characterized in that the second component A-2 contains at least twice as much compound T as the first component A-1, based on the molar amount of thiol groups of compound T in the respective component.

7. Three-component polyurethane composition according to one of the preceding claims, characterized in that the polyol P comprises at least one polyethertriol.

8. Three-component polyurethane composition according to one of the preceding claims, characterized in that the polyisocyanate I comprises a liquid form at room temperature of 4,4'-, 2,4'- or 2,2'- diphenylmethane diisocyanate and any mixtures of these isomers (MDI) in the form of polymeric MDI or MDI with proportions of oligomers or derivatives, in particular carbodiimides.

9. Three-component polyurethane composition according to one of the preceding claims, characterized in that the third component B contains an isocyanate group-containing polyurethane polymer.

10. Three-component polyurethane composition according to one of the preceding claims, characterized in that at least the third Component B contains at least one drying agent, preferably also at least one of components A-1 and A-2.

11. A method for bonding at least three substrates layer by layer, comprising the steps in the following order: a) providing the first component A-1, the second component A-2, and the third component B according to any one of claims 1 to 10, wherein each of the three components is connected to a mixing chamber via its own pump and can be conveyed separately; b) conveying the required quantity of the first component A-1, the second component A-2, and the third component B to the mixing chamber and mixing the components by a static or dynamic mixer, wherein the mixing ratio of components A-1, A-2, and B is controlled by the delivery rate of the respective pump and is set before the mixing process and optionally corrected during the mixing process; c) applying the mixed polyurethane composition from the mixing chamber to the surface of one of the substrates to be bonded; d) joining another substrate onto the applied adhesive;e) Repeat steps b) to d) until all substrates are joined layer by layer using adhesive, using a higher proportion of the first components A-1 and a lower proportion of the second components A-2 in each subsequent bonding operation than in the previous one; f) optionally, press the joined substrates together within the pot life of all applied adhesive layers until the adhesive layers have cured sufficiently to allow the bonded substrates to be moved.

12. Method according to claim 11, characterized in that the application of the mixed polyurethane composition is carried out fully automatically by means of a robot or 3D printer.

13. Method according to one of claims 11 or 12, characterized in that the mixing ratio of components A-1, A-2 and B is calculated in advance for each adhesive layer, taking into account the ambient temperature during the execution of the method when calculating the mixing ratio.

14. Method according to one of claims 11 to 13, characterized in that the mixing ratio of components A-1, A-2 and B for each adhesive layer is calculated by a computer during the method and adjusted as necessary, wherein parameters are measured via at least one sensor during the method, which are read into the computer and which have an influence on the calculation of the mixing ratio.

15. Method according to claim 14, characterized in that the parameters are selected from ambient temperature, humidity, temperature of components A-1, A-2 and / or B or the mixed composition, substrate temperature, and substrate moisture.

16. Method according to one of claims 11 to 15, characterized in that the substrates are wooden boards.

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