2-component structural adhesives

Abstract

The present invention relates to new formulations for 2-component structural adhesives based on aliphatic polyisocyanates and linear polyether aspartic acid esters of comparatively short chain length or comparatively low molecular weight, for adhesively bonding identical or different substrates. The invention further relates to the use of this formulation for structurally adhesively bonding substrates, in particular technical plastics, in particular in industrial applications. The invention also relates to corresponding processes and to the resulting system composed of at least two substrates and of a structural adhesive bond containing the cured formulations according to the invention.

Description

2-component structural adhesives The present invention relates to new formulations for 2-component structural adhesives based on aliphatic polyisocyanates and linear polyether aspartic acid esters of comparatively short chain length or comparatively low molecular weight, for bonding identical or different substrates. Reactive two-component adhesives are increasingly used for the structural bonding of substrates. In structural bonding, identical or different substrates are permanently joined together, with the bonded component fulfilling a structural function. To distinguish them from elastic sealants, structural adhesives are defined in the present application according to DIN EN 923:2016-03 as adhesives suitable for the production of load-bearing structures, whereby the adhesive bond can be stressed or loaded for a longer period of time without failure of the structurally bonded connection within the scope of the respective application. Structural adhesives possess high internal strength (cohesion) and at the same time good adhesion to the substrate. In accordance with the definitions of DIN EN 923:20216-03, structural adhesives differ fundamentally from aqueous dispersion adhesives and solvent-based pressure-sensitive adhesives. Unlike single-component adhesives or sealants, the curing of two-component structural adhesives depends solely on temperature and is essentially independent of humidity or oxygen. The following product groups, among others, have become established as two-component structural adhesives in the state of the art: • 2-component epoxy resin adhesives comprising a polyepoxide component and a polyamine and / or polymercaptan component Two-component acrylate adhesives comprising acrylate copolymers that are radically cured with a peroxide component. • 2-component polyurethane adhesives comprising a polyisocyanate component and a polyol and / or polyamine component Two-component polyurethane adhesives can be formulated in various ways and are therefore particularly versatile as structural adhesives. Due to their high reactivity, reactive structural adhesives predominantly use aromatic polyisocyanates in combination with various polyols such as polyester polyols, polyether polyols, polycarbonate polyols, and / or low-molecular-weight polyalcohols. However, the aromatic monomeric diisocyanates diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI) possess carcinogenic properties, which strictly limits their use. The hydrolysis products of these monomeric diisocyanates, aromatic diamines, are also carcinogenic and are released from the adhesives through migration. Nowadays, therefore, low-monomer polyisocyanates based on TDI and / or MDI are preferred. These are produced by oligomerization or prepolymerization of these isocyanates and subsequently freed from monomeric diisocyanates by thin-film distillation. However, the polyisocyanates and / or isocyanate prepolymers obtained in this way are often highly viscous or resinous, so that they can generally only be processed into adhesives with the aid of solvents or plasticizers, which is disadvantageous from both an adhesive technology and environmental perspective. Therefore, adhesives based on aliphatic, low-monomer polyisocyanates derived from isophorone diisocyanate and / or hexamethylene diisocyanate, which are physiologically relatively favorable, have been increasingly formulated recently. Such adhesives typically contain the polyols mentioned above as a second component. These aliphatic two-component polyurethane adhesives generally have a significantly lower reactivity compared to aromatic isocyanates, so catalysts must usually be added to accelerate curing. Typical catalysts used are... For example, toxic organotin compounds or strongly basic tertiary amino compounds. Despite the use of the aforementioned catalyst systems, the curing rate of these polyol systems is insufficient or at least in need of improvement for many modern applications. A comparatively rapid curing process can be achieved by partially or completely replacing the aforementioned polyols with aromatic polyamine compounds. The polyaddition of the aromatic amines with the polyisocyanates occurs within minutes, allowing the formulation of structural adhesives with sufficiently rapid assembly strength using this technology. Disadvantages of these polyamine-based adhesives include their strong tendency to yellow and their poor reactivity at temperatures below approximately 5°C. An overview of the advantages and disadvantages of various adhesives can be found, for example, in "Bodo Müller and Walter Rath, Formulation of Adhesives and Sealants", 3rd edition, Vincenz Network 2015, p. 107 ff. An improvement over the prior art can be achieved if polyaspartic acid esters based on aliphatic and / or cycloaliphatic diamines are used instead of aromatic amines, as described in patent applications EP 3 749 730 B1 and WO 2021 / 023841 A1. Two-component coating systems based on aliphatic polyisocyanates and amino-functional aspartic acid esters, such as those formed by the addition of maleic and / or fumaric acid esters to polyamines, have been known in principle for some time, but only as varnishes and in coating systems, and are described by way of example in the following patent applications: EP 3 098 247 A1 and EP 3 115 388 A1. Polyaspartic acid esters based on polyetheramines and their use in combination with aliphatic polyisocyanates are also generally known, but again only in coating systems (see e.g. EP 3 626 755 A1 , WO 2014 / 151307 A1 , WO 2022 / 253635 A1 , WO 2020 / 260578 A1 or WO 2022 / 136554 A1). Coating systems, however, differ fundamentally from adhesives, especially structural adhesives. Formulations known from coating technology are not considered by those skilled in the art for structural bonding. Instead, for structural bonding, those skilled in the art consider the aforementioned classes of two-component structural adhesives. There are fundamentally significant differences regarding the application and properties of adhesives, especially structural adhesives, on the one hand, and coatings on the other: Coatings are applied in a relatively thin layer to a (single) substrate by spraying, brushing, dipping, or squeegeeing and fulfill functional and decorative purposes. Adhesion to the substrate (see above: "adhesion") is an essential quality characteristic and is achieved in most cases by pretreating the substrate or applying adhesion promoters. The most important properties of a coating are characterized in particular by the following properties: adhesion tested by cross-cut test (ISO 2409) or tensile test (ISO 4624), hardness tested by pencil hardness test (ISO 15184) or pendulum hardness test (ISO 1522), gloss and color tested by gloss measurement (ISO 2813) and color measurement (ISO 18314), weather resistance tested by outdoor weathering test or QUV test (ISO 16474) and deformability, tested by Erichsen indentation test (DIN 1520). Adhesives, on the other hand, are used to join two identical or different substrates. The quality of the bond depends on the adhesion to the substrates and the inherent strength of the bond. This overall strength is determined primarily through tensile tests and verified according to DIN EN 1465 (2009-07), which depends on the structural bond and the substrate. The tensile strength of a bond characterizes its strength on a specific substrate and is unrelated to the tensile strength of polymers or polymeric coating films. As explained above, the known two-component structural adhesives have various disadvantages and are certainly not equally (well) suited for all applications. In particular, in the field of structural bonding in industrial applications, there is a lack of formulations that exhibit a broad adhesion spectrum, i.e., those that can bond to a wide range of materials. a wide variety of substrates, including those that are difficult to bond, can be applied and result in durable bonds. The inventors have found that the constructive bonding of substrates in general and technical plastics in particular, including acrylate plastics - especially polymethyl methacrylate - or polyethylene terephthalates, is not satisfactorily achieved with existing adhesive systems, but is with the claimed ones. Within the scope of the present disclosure are “engineering plastics” Engineering plastics (also known as technical plastics or construction materials) are a subgroup of thermoplastic polymers and are typically distinguished from "standard plastics" by their properties and price. Compared to standard plastics, engineering plastics possess improved mechanical properties such as higher impact strength or higher moduli of elasticity and are therefore suitable for technical applications and, in some cases, structural applications (load-bearing components). The object of the present invention is therefore to provide an improved formulation for bonding substrates, particularly in the context of industrial processes (with predetermined cycle times). Another task is to provide formulations for 2-component structural adhesives that can be processed in a wide temperature range, as well as having sufficiently long "pot lives" (time window within which the 2-component structural adhesive can be processed) and / or sufficiently short time periods until the "assembly strength" is reached (period after which further processing is possible after application). Another task is, in particular, the bonding of technical plastics as substrates. This task and others are solved using the following formulation: Formulation for a 2-component structural adhesive for structural bonding of identical or different substrates, wherein this formulation contains at least: (i) at least one polyisocyanate having free isocyanate groups a content of aliphatic-bound NCO groups of 16.0 to 24.0 wt.%, (ii) at least one amino-functional polyaspartic acid ester of the general formula where R 1 and R 2 independently of each other, representing a methyl or an ethyl group; and where X represents a divalent organic residue obtained by removing the amino groups from aminopolyether of the general structural formula and isomers thereof, where n is a number in the range of 2 to 8, as well as (iii) optionally at least one filler, excipient or additive. In preferred embodiments, X represents a divalent organic residue obtained by removing the amino groups from aminopolyether, wherein the aminopolyether contains 9 to 27 carbon atoms and 2 to 8 oxygen atoms. In preferred embodiments, a formulation according to the invention, after mixing all components and before application to a substrate, has a viscosity at 23°C according to DIN EN 12092:2001 in the version of February 2002 in the range of 1000 mPa s to 400,000 mPa s, preferably from 2000 mPa s to 200,000 mPa s, more preferably from 5000 mPa s to 200,000 mPa s. The comparatively high viscosity values ​​according to the invention can be adjusted via the reactants i) and ii) themselves (e.g. by using highly viscous isocyanates), and / or via the addition of auxiliary substances iii) such as silica. In contrast, formulations for coatings typically have lower viscosity values ​​of less than 200 mPa s at 23°C. The viscosity is determined according to the invention in accordance with DIN 12092:2001 (February 2002), specifically using the rotational viscometer method described in section 6.2 (pages 4 and 5). The viscometer used is the standard Brookfield DVNext RV viscometer (https: / / www.brookfieldengineering.com / products / viscometers / laboratory-viscometers / dvnext-rheometer). The test temperature is 23°C, and the rotational speed is 10 rpm. The appropriate spindle (RV02-RV07) is selected depending on the viscosity range; for pasty, filler-containing mixtures, spindle V74 or V75 is used, depending on the viscosity range; the measured values ​​are taken 5 minutes after mixing. The comparatively high viscosity according to the invention (especially compared to coatings) is advantageous for the application of the 2-component structural adhesive on one or more substrates, particularly when these substrates are not in a horizontal position ("stability"). In preferred embodiments, n is a number from 2.5 to 6.5, more preferably from 2.5 to 4.5. In these ranges, a particularly good ratio of flexibility to internal strength is achieved. It was surprisingly discovered that, using amine-functional aspartic acid esters, especially based on the short-chain linear polyetheramines disclosed and claimed here, structural adhesive formulations with a particularly broad adhesion spectrum (i.e., good adhesion to different substrates, including steel and wood, and especially engineering plastics) can be obtained. Compared to known two-component structural adhesives, the formulations according to the invention can achieve, in particular, improved adhesion to engineering plastics, for example, acrylate plastics. Permanently load-bearing structural bonding of engineering plastics is therefore possible. their intrinsic flexibility and comparatively low surface energy often pose problems. The inventors further found that the short-chain polyether aspartates according to the invention exhibit good adhesion to substrates, with a favorable ratio of flexibility to internal strength. Longer-chain polyether aspartates, on the other hand, are often too flexible and unreactive. Further advantages of 2-component structural adhesives as disclosed and claimed herein include a comparatively fast curing without layer thickness limitations, as well as the freedom from significant amounts of organic solvents or water in the adhesive formulation. Furthermore, when using the formulations disclosed and claimed herein, the processing time (“pot life”) is sufficiently long and variably adjustable, so that these formulations can be advantageously used as 2-component structural adhesives in industrial processes with predetermined and repetitive cycle times or in processes in which larger quantities of adhesive formulation are applied. The pot life is measured according to DIN EN ISO 10364:2024 (April 2024), specifically using method 5 based on the string break time (see section 6.6 on pages 11 and 12 of the DIN standard). The temperature is 23°C, the volume is 30 ml, and the two components are mixed in the specified mixing ratio. Finally, when using the formulations disclosed and claimed here for 2-component structural adhesives, despite a comparatively long pot life, the time from which the bond can be loaded or further processed ("strength", "assembly strength", "handling strength") is comparatively short, e.g. only 3 - 4 times longer than the pot life. According to the website of the German Adhesives Association (https: / / leitfaden.klebstoffe.com / 4-3-handwiderstand / ), "handling strength" (or "assembly strength") describes the strength that allows further processing of a bonded component without additional fixation; that is, the fixative can be removed at this point. Adhesive manufacturers determine handling strength by measuring the required strength of the adhesive. a specific strength value (usually between 0.2 and 1 MPa) or a specific percentage of the final strength is specified. Handling strength is also called handling strength or "handling" strength. The 2K structural adhesives that can be used in the method according to the invention cure quickly and can be formulated in such a way that, depending, for example, on the presence or absence of catalysts of component iii) - in particular water - they have a comparatively long pot life of 5 minutes to 100 minutes, preferably from 10 minutes to 75 minutes, and achieve assembly strength / handling strength in a comparatively short period of 20 minutes to 200 minutes, preferably from 30 minutes to 150 minutes. In preferred embodiments, the formulations disclosed and claimed herein, comprising components i), ii) and iii), are further characterized as follows. Aliphatic polyisocyanates that can be used as component i) are known in principle and are produced by means of suitable modification reactions, such as dimerization, trimerization, biuretization, allophanatization and / or urethanization of hexamethylene diisocyanate and / or isophorone diisocyanate, preferably exclusively of hexamethylene diisocyanate, wherein excess monomeric diisocyanate is subsequently removed from the mixture by distillation. In preferred embodiments, the aliphatic polyisocyanates of component i) have low residual contents of monomeric diisocyanate, preferably <0.5 wt.%, preferably <0.3 wt.%, particularly preferably <0.1 wt.%, in each case based on the total weight of the polyisocyanate mixture in component i). Preferably, the polyisocyanates used as component i) are derivatives of HDI containing uretdione, isocyanurate, iminooxadiazindione, urethane, allophane, biuret and / or oxadiazintrione groups, which have a viscosity of 200 to 20,000 mPas at 23°C, and more preferably an isocyanate group content of 16 to 24 wt.%, preferably 17 to 23.5 wt.% and an average isocyanate functionality of at least 2.5, preferably at least 3.0. Particularly preferred as component i) are polyisocyanates based on hexamethylene diisocyanate with biuret structures and / or isocyanurate structures and / or iminooxadiazinde ion structures. In a preferred embodiment of the present invention, polyisocyanate mixtures containing alkoxysilane groups are used as component i). Such polyisocyanate mixtures can be obtained, for example, by reacting polyisocyanates with functional silanes that have a functional group which can react with the isocyanate groups of the polyisocyanates, or by special processes as described by way of example in DE 10 2009 047964 A1 and DE 10 2007 032666 A1. The polyisocyanates that can be used as component i) in the process according to the invention can be mixed with isocyanate prepolymers with a view to adjusting the mixing ratios of the processable 2-component mixture. Examples include isocyanate prepolymers known from polyurethane technology, which are produced by reacting aliphatic di- or polyisocyanates with higher molecular weight polyols, in particular polyether polyols, polyester polyols or polycarbonate polyols. In this process, preferably subordinate amounts of isocyanate prepolymers are used for mixing, wherein the mixtures correspond to the above specifications regarding isocyanate content and residual monomer content. The amounts of isocyanate prepolymers are preferably less than 20 wt.% based on the total weight of component i), preferably less than 10 wt.%, particularly preferably less than 5 wt.%. Components ii) in the formulations according to the invention comprise at least one amino-functional polyaspartic acid ester of the general formula where R 1 and R 2 independently of each other, representing a methyl or an ethyl group; and where X represents a divalent organic residue obtained by removing the amino groups from aminopolyether of the general structural formula and isomers are obtained from this. Here, n is 2 to 8, preferably 2.5 to 6.5, particularly preferably 2.5 to 4.5. Preferably, X represents a divalent organic residue obtained by removing the amino groups from aminopolyether, wherein the aminopolyether contains 9 to 27 carbon atoms and 2 to 8 oxygen atoms. The preparation of the amino-functional polyaspartic acid esters ii) is preferably carried out by reacting technical mixtures of polyoxypropylenediamines of the above-mentioned structural formula, containing corresponding constitutional isomers preferably in subordinate amounts, with maleic or fumaric acid dimethyl ester and / or maleic or fumaric acid diethyl ester, preferably with maleic or fumaric acid diethyl ester. The preparation of the amino-functional polyaspartic acid esters ii) from the aforementioned starting materials is preferably carried out within the temperature range of 0 to 100°C, wherein the starting materials are used in such proportions that each primary amino group is represented by at least one, preferably exactly one, olefinic double bond, and wherein, following the reaction, any excess starting materials used can optionally be separated by distillation. The reaction is preferably carried out in bulk, but can also be performed in the presence of suitable solvents such as methanol, ethanol, propanol, or dioxane. Mixtures of such solvents are used, with the co-use of solvents being less preferred. In the formulations according to the invention, the amino-functional polyaspartic acid esters ii) that can preferably be used are purified by distillation and contain diethyl fumaric acid esters in amounts of less than 0.2 wt.% based on the total weight of component ii), preferably less than 0.1 wt.%. In preferred embodiments, the formulation according to the invention is present in mixture with at least one amino-functional polyaspartic acid ester based on aminopolyethers according to ii) as defined above, and with at least one other isocyanate-reactive substance, wherein the following applies: • the amino-functional polyaspartic acid ester based on amino polyethers and at least one other isocyanate-reactive substance are both present together as a mixture in component ii), • wherein at least 10 wt %, preferably at least 20 wt %, further preferably at least 40 wt %, further preferably at least 60 wt %, of the total mixture in component ii) are the polyaspartic acid esters according to the invention based on aminopolyethers. The above-mentioned advantages of this mixture are fully realized only if, in addition to these other isocyanate-reactive substances, significant amounts of the amino-functional polyaspartic acid ester according to the invention based on aminopolyethers according to ii) are present, in particular at least 10 wt.% or at least 20 wt.% of the above-mentioned amounts. Depending on the application, it may be desirable to add to the comparatively slow-curing amino-functional polyaspartic acid esters based on amino polyethers according to ii) comparatively faster-curing polyaspartic acid esters based on linear-aliphatic or cycloaliphatic diamines, as disclosed in patent applications EP 3 626 755 A1, WO 2014 / 151307 A1, and WO 2022 / 253635 A1. The curing time can thus be precisely and flexibly adjusted using the preferred mixture according to the invention. It is preferred that the at least one other isocyanate-reactive substance is a polyaspartic acid ester of the general formula as described above, wherein X represents a divalent organic residue obtainable by removing the amino groups from diamino-dicyclohexylmethane or a straight-chain or branched aliphatic diamine, preferably having up to 9 carbon atoms. Preferred in this context are polyaspartic acid esters based on 2-methyl-1,5-diaminopentane and diethyl maleate and diamino-dicyclohexylmethane and diethyl maleate. Furthermore, low molecular weight polyols such as 1,2-ethanediol, 1,2-propanediol, 1,4- or 1,3-butanediol, 1,6-hexanediol, 2-ethylhexanediol-1,3, 1,8-octanediol, glycerol or dimer fatty alcohols or castor oil are preferred over other isocyanate-reactive substances mentioned above. Also suitable for use are diols containing ether groups, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol or mixtures of such alcohols, as well as ethoxylation and / or propoxylation products of aliphatic mono- and diamines or amino alcohols such as triethanolamine, N-methyl-diethanolamine or N,N-dimethylethanolamine. In further embodiments, higher molecular weight polyols can be used as other isocyanate-reactive substances within component ii). These include, in particular, hydroxy-functional polyether polyols, polyester polyols, polycarbonate polyols, and mixtures of the aforementioned polyols. The other isocyanate-reactive substances mentioned above are preferably used in a mass fraction of less than 90 wt.%, preferably less than 80 wt.%, further preferably less than 60 wt.%, and particularly preferably less than 40 wt.% based on the total weight of component ii). According to the invention, mixtures of the above-mentioned other isocyanate-reactive substances can also be used within component ii). The formulations according to the invention for 2-component structural adhesives can further contain fillers, auxiliary or additives (“adjuvants”) suitable as component iii) in adhesive technology. Such additives include, in particular, catalysts, inorganic and organic fillers, flame retardants, pigments, leveling agents, thixotropic agents, solvents, plasticizers, and other viscosity regulators. These additives are used to adjust the application properties of the two-component structural adhesive for the specific application required. Solvents may optionally be used as component iii) to improve substrate wetting in small quantities, i.e. in quantities of less than 2 wt.%, preferably less than 1 wt.% based on the total weight of the structural adhesive. In preferred embodiments, the formulation according to the invention for 2-component structural adhesives comprises less than 2 wt.%, more preferably less than 1 wt.%, of organic solvents. The fact that the formulations according to the invention can also be formulated without or, if necessary, with small amounts of solvents for use in structural bonding is advantageous from a cost and environmental perspective. Suitable solvents present in the aforementioned small quantities include, in particular, ethyl acetate, butyl acetate, methoxypropyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, aromatic or (cyclo-)aliphatic hydrocarbon mixtures, or any mixtures of such solvents. In a preferred embodiment of the present invention, the structural adhesives contain fillers as component iii). Suitable fillers include sands, rock flour, quartz flour, talc, natural, ground or precipitated calcium carbonates, which may be coated with fatty acids, barium sulfate (BaSO4, also called barite or barite), soot, and silicas, preferably highly dispersed silicas from pyrolysis processes. Preferred fillers are talc and silica, which are particularly preferred in combination. Such fillers are also suitable for adjusting desired viscosity ranges. These and all other conceivable fillers can be incorporated into both component i) and component ii). Aluminum hydroxide and magnesium hydroxide are preferred as powdered flame retardants within component iii). Aromatic and aliphatic esters of phosphoric acid are preferred as liquid flame retardants within component iii). In principle, all organic and inorganic pigments known from coating technology, preferably in paste form, can be used as component iii). Such pigments can be incorporated into both component i) and component ii). To generate sufficient adhesion on certain “problematic” substrates, the formulations according to the invention for 2K structural adhesives can, in preferred embodiments, contain functional silanes as part of component iii). In this context, y-organofunctional silanes and a-organofunctional silanes are preferred. Particularly preferred are 3-mercaptopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, N-alkyl-3-aminopropyltrimethoxysilane, N-aminoethyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and the corresponding triethoxysilane derivatives and dimethoxymethyl derivatives of the aforementioned functional silanes. Further preferred as silanes are tris-[3-(trimethoxysilyl) propyl]-isocyanurate and N-methyl[3-(T rimethoxysilyl)propyl]carbamate, methacryloxymethyl-trimethoxysilane, N-trimethoxysilylmethyl-O-methylcarbamate. Of course, mixtures of silanes can also be used within component iii). The named functional silanes are preferably used in amounts of less than 2 wt.%, preferably less than 1 wt.%, based on the total weight of the adhesive formulation. To adjust the reaction rate, the 2K structural adhesives according to the invention can, in preferred embodiments, contain catalysts as component iii). In this context, preferred are the catalysts known from aspartic acid ester technology and in particular those known from EP 2 673 310 B1, such as water or tertiary amines, for example triethylamine, dimorpholinodiethyl ether, N,N-dimethylaminocyclohexane, tris-(dimethyl-aminomethyl)phenol, 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine, bis(dimethylamino-ethyl) ether, 2-[[2-[2-(Dimethylamino)ethoxyethyl]methylamino]ethanol. Further preferred catalysts within component iii) are metal salts of zinc, tin, zirconium, and bismuth, preferably bismuth. Bismuth neodecanate is particularly preferred as a catalyst within component iii). Further preferred catalysts within the scope of the present invention are carboxylic acids such as formic acid, acetic acid, propionic acid or benzoic acid, as well as dicarboxylic acids such as oxalic acid or malonic acid. In a particularly preferred embodiment of the present invention, the 2K structural adhesives according to the invention contain water as a catalyst, as a component of component iii). Preferably, the 2K structural adhesives according to the invention contain, within component iii), 0.05 to 2.5 wt.% water based on the total weight of the adhesive formulation, particularly preferably 0.05 to 1 wt.% water. The 2K structural adhesives according to the invention basically contain only catalytic amounts of water, or no water at all. The water used does not serve the purpose of a solvent. The 2K structural adhesives according to the invention therefore differ fundamentally from aqueous dispersion or emulsion adhesives according to DIN EN 923:2016-03. According to the invention, mixtures of the above-mentioned catalysts can also be used within component iii). Aromatic and / or aliphatic polyamines, preferably aliphatic polyamines, are also preferred within component iii). Preferred polyamines are diethyltoluenediamine, dimethylthiotoluenediamine, ethylenediamine, 1,2-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 2,5-diamino-2,5-dimethylhexane, 2,2,4- and / or 2,4,4-trimethyl-1,6-diaminohexane, 1,11- Diaminoundecane, 1,12-Diaminododecane, 1-Amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 2,4- and / or 2,6-hexahydrotoluenediamine, 2,4'- and / or 4,4'-Diamino-dicyclohexylmethane or 3,3'-Dimethyl-4,4'-diamino-dicyclohexylmethane and polyetheramines of the prior art. Such polyamines react significantly faster than the aspartic acid esters of the Component ii) and are incorporated into it. Due to the rapid reaction of the polyamines, a rapid viscosity increase occurs immediately after application. Therefore, the polyamines of the type mentioned below as examples can be formulated, in particular for rheology control. Such polyamines are preferably used as additives in a mass fraction of up to 5 wt.%, particularly preferably up to 2 wt.% based on the total weight of the adhesive formulation as component iii). Further auxiliary and additive agents (iii) include deaerating agents, defoamers, flow agents, and antioxidants. Antioxidants in this context include antioxidants, UV absorbers, and free radical scavengers, as well as corresponding combinations of these antioxidants. For the formulation of the inventive formulation for 2K structural adhesives, components i), ii) and iii) are preferably used in a ratio such that the equivalent ratio of the isocyanate groups of component i) to the amino and / or alcoholic hydroxy groups of components ii) and iii) is 0.9:1 to 1.8:1, preferably 1.1 to 1.5:1. The 2K structural adhesives that can be used in the process according to the invention preferably contain a mass fraction of 25 to 55 wt.%, preferably 30 to 50 wt.% of component i), a mass fraction of 20 to 55 wt.%, preferably 30 to 50 wt.% of component ii), and a mass fraction of 0 to 40 wt.%, preferably 1 to 30 wt.% of component iii). These preferred quantity ranges combine advantageous adhesion (tensile shear strength) and mechanical properties (flexibility). The 2K structural adhesives that can be used in the inventive method can be adjusted from low viscosity to high viscosity with regard to processing viscosity. Low-viscosity formulations are used when substrates are to be bonded virtually gap-free, i.e. with a gap of less than 0.1 mm; higher-viscosity formulations are used when bonding with a larger gap is required. The formulations according to the invention for 2K structural adhesives are formulated as 2-component systems comprising a resin component and a hardener component. The formulation is preferably carried out such that the components iii) are incorporated into the components i) and ii) in the sense of viscosity equalization, with the restriction that catalysts and isocyanate-reactive compounds iii) are preferably incorporated exclusively into the component ii). Preferably, the formulation is such that two-component systems are obtained with a volume ratio of 20:80 to 80:20, preferably 60:40 to 40:60, and particularly preferably 50:50 for the ratio of resin component to hardener component. The two-component structural adhesives that can be used in the process according to the invention are highly reactive and can typically only be processed with the aid of suitable two-chamber dispensing systems. Preferred dispensing systems are 2K cartridge systems in conjunction with suitable static mixers, as exemplified in WO 2011 / 162728 and the secondary literature cited therein. Particularly preferred within the scope of the present invention are double cartridge systems with child safety lock, as described in the German utility model application DE 2020 16102271 (U1). It is further preferred, either alone or in combination with the or all of the above-mentioned parameters, that the formulation according to the invention, in the cured state, i.e. after mixing and application of all components, and after curing, i.e. after at least 24 hours after mixing and application, has a tensile shear strength according to DIN EN 1465 (2009-07) of at least 7 MPa, preferably at least 10 MPa, as measured between two test specimens on roughened V2A steel. The tensile shear strength is determined at 23°C, as shown in the examples below and in EP 3 749 730 in the paragraphs

[0107] and

[0108] described, the corresponding revelation of which is part of the present revelation. High tensile shear strengths in the stressed area are advantageous for bonding between substrates, as permanently stable and resilient structures are obtained, especially in the field of industrial applications. In a further aspect which solves the above-mentioned problems, or parts thereof, the present invention relates to the use of the above-described formulation, in all embodiments as described herein, for the structural bonding of two substrates, in particular substrates containing engineering plastics. In a further aspect which solves the above-mentioned problems, or parts thereof, the present invention relates to a method for structurally bonding at least two substrates, wherein the method comprises at least the following steps: (a) Providing a formulation for a two-component structural adhesive as described herein; (b) Application of the formulation from (a) to at least one substrate; (c) Bonding of at least two substrates, one of which is the substrate from (b). Another aspect that solves the aforementioned tasks, or parts thereof, concerns a system comprehensively: (1) At least two substrates joined by a cured two-component structural adhesive based on a formulation for a two-component structural adhesive as described herein; (2) said cured 2-component structural adhesive. In preferred embodiments, the gap dimension, i.e. the thickness of the structural adhesive layer between the two substrates, is from 1 pm to 1 cm, preferably from 50 pm to 2 mm. The 2K structural adhesives that can be used according to the invention exhibit excellent adhesion to application-relevant organic and inorganic substrates such as wood and wood-based materials, steel, aluminum, concrete, glass, leather, keratin or paper, even without the addition of special adhesion promoters such as the functional silanes of the type mentioned above. In a further advantage over state-of-the-art structural adhesives, the formulations for 2-component structural adhesives described and claimed herein surprisingly show a significantly improved adhesion to engineering plastics such as, in particular, polyethylene terephthalate (PET), glycol-modified polyethylene terephthalate (PETG), and polymethyl methacrylate (PMMAi). The adhesion to other organic substrates, in particular plastics, or inorganic substrates, in particular metals and metal alloys, can be specifically controlled by adding the substances suitable above within the scope of component iii). Thus, the formulations according to the invention represent a significant advance in the constructive joining of identical or different plastics or in the bonding of plastics to metals. To achieve sufficient adhesion, it may be advantageous in the inventive method to prepare the substrate accordingly. This can be done by mechanical pretreatment such as roughening or sanding, but also by chemical pretreatment such as plasma or corona treatment, or by applying primers and adhesion promoters. Suitable primers include, for example, solutions of the functional silanes mentioned above as component iii) in organic solvents, or solutions of chlorinated polyolefins and / or modified chlorinated polyolefins in organic solvents. Such solutions of chlorinated polyolefins are particularly useful as primers when sufficient adhesion to nonpolar plastics, especially polyolefin plastics such as polypropylene, is required. The aforementioned chlorinated polyolefins or modified chlorinated polyolefins preferably have a chlorine content of 10 to 25 wt.%, based on the Solid fraction of the chlorinated polyolefins. Preferably, the chlorinated polyolefins or modified chlorinated polyolefins used have a number-average molecular weight of 8,000 to 50,000. The amount of chlorinated polyolefins used in a primer formulation is preferably 0.2 to 5.0 wt.%, based on the total weight of the primers and the solids content of the chlorinated polyolefins, respectively. The chlorinated polyolefins used according to the invention are known to those skilled in the art and are commercially available, for example, under the trade names Eastman™ chlorinated polyolefins from Eastman Chemical Products, Inc., Trapylen from Tramaco, or Hardlen from Toyo Kasei. Within the scope of the present invention, it has been observed that adhesive formulations according to the invention enable the production of bonds with surprisingly high internal strengths, as can be measured, for example, by the tensile shear strength of a cured structural bond between two substrates. The tensile shear strength is determined here according to the standard DIN / EN 1465 (2009-07) for various substrates. As mentioned above, paints and coatings differ fundamentally from structural bonding. This also results from their different performance parameters. The tensile strength parameter commonly used for coatings indicates the maximum mechanical tensile stress that a (polymer) material can withstand. This value can also be determined for coatings and adhesives (according to DIN EN ISO 527 and DIN 53504 for elastomers, respectively). For this test, the latter are cast into a bone-like mold and, after curing, pulled apart longitudinally until the mold breaks. This measures a material property of the polymer (the material's strength). However, it provides no information about the polymer's adhesion behavior to other materials, as adhesion involves significant forces between the polymer and the substrate, which are not considered when determining tensile strength. To determine the parameter tensile shear strength, as used in the adhesive field and described above, two substrates are tested using a The substrate is bonded with a structural adhesive and tensioned longitudinally until fracture. In this test, the applied force acts on the substrate, the adhesive, and—most importantly—the bond between the adhesive and the substrate. The resulting structural strength depends on the cohesion of the substrates and the adhesive, as well as on the adhesion between the adhesive and the substrate. Here, all the important interactions of an adhesive bond are considered in a single parameter. Within the scope of the present invention, it was further observed that with the formulations according to the invention, bonds with surprisingly high internal strengths can be produced, so that bonds with a gap of less than 0.1 mm and up to 1 cm can be produced with high strength. The two-component structural adhesives according to the invention can be processed within a wide temperature range. They cure reliably in a temperature range from -20°C to +50°C. Furthermore, the cured adhesives exhibit outstanding impact strength at low temperatures down to -40°C and simultaneously possess excellent high-temperature resistance in the temperature range up to 150°C. The following examples are intended to illustrate the invention without limiting its scope. A comparison of the examples according to the invention with examples not according to the invention is intended to clarify the technical advantages of the method according to the invention. Examples that do not fall within the scope of the claimed subject matter are for comparison purposes only. Production of aspartic acid esters based on polyetheramines Polyether aspartic acid ester 1 430 g of Jeffamin D400 (polyetheramine from Huntsman, according to the formula above with n = 6.1) are added dropwise to 344 g of diethyl maleate at 40°C while stirring. The reaction mixture is stirred for 8 hours at 40°C and then for a further 24 hours at room temperature. After a storage period of 30 days, the reaction is largely complete and the This product can be used to formulate adhesives. The reaction product has an NH equivalent weight of 387. Polyether aspartic acid ester 2 230 g of Jeffamin D230 (polyetheramine from Huntsman, according to the formula above with n = 2.5) are added dropwise to 344 g of diethyl maleate at 40°C while stirring. The reaction mixture is stirred for 8 hours at 40°C and then for a further 24 hours at room temperature. After a storage period of 30 days, the reaction is largely complete and the product can be used for formulating adhesives. The reaction product has an NH equivalent weight of 287. Polyether aspartic acid ester 3 One part by weight of polyetheraspartic acid ester 1 is mixed with three parts by weight of polyetheraspartic acid ester 2. This results in a polyetheraspartic acid ester with an NH equivalent weight of 312, corresponding to n = 3.4. Polyether aspartic acid ester 4 Desmophen NH 1723, commercially available polyaspartic acid ester from Covestro AG, Leverkusen, with an NH equivalent weight of 295 corresponding to n = 2.85, residual content of diethyl fumaric acid ester <0.1 wt.%. Polyisocyanate 1 Commercially available polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 3000 mPas (23°C), residual monomer content <0.1%, Desmodur N3300 Ultra, a commercial product of Covestro AG, Leverkusen Polyisocyanate 2 Commercially available polyisocyanate based on hexamethylene diisocyanate with an iminooxadiazindione structure and an NCO content of 23.5% and a viscosity of 700 mPas (23°C), residual monomer content <0.1%, Desmodur N3900, a commercial product of Covestro AG, Leverkusen Polyisocyanate 3 Commercially available polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 20.0% and a viscosity of 16,000 mPas(23°C), residual monomer content <0.1%, Desmodur N3700 Ultra, a commercial product of Covestro AG, Leverkusen. General instructions for the production of components A and B Unless otherwise described, all mixtures of components A and B in the 2-component system were prepared in a Hausschild brand speed mixer. For this purpose, the individual components, starting with the liquids, were weighed into suitable containers and mixed for 30 seconds at 1800 rpm. The solids were then added and dispersed for 5 minutes at 2000 rpm. Both components (A and B) were then degassed during a second dispersion in the speed mixer using a vacuum pump to remove air bubbles. application For application, components A and B were filled into a 2K cartridge – DK50.2GLUE.PP.W from Gluetec Industrieklebstoffe GmbH & Co. KG. Application was carried out in a 1:1 volume ratio using a Gluetec 2K mixer MXD25-37-50t from Gluetec Industrieklebstoffe GmbH & Co. KG. The two-component adhesives were applied to one side of cleaned test specimens measuring 100 mm in length and 25 mm in width to determine the tensile shear strength in accordance with DIN EN 1465:2009-07. Bonding was then performed over an overlap length of 12.5 mm with a gap of 0.1 mm. The gap was adjusted by inserting spacers of the desired layer thickness in the unwetted area of ​​the test specimens. The pot life was measured in accordance with DIN 10364 using the string-break method (see above), in which strings are pulled from a defined quantity of mixed formulation at regular intervals using a wooden spatula. The pot life is reached as soon as no more long strings are formed. can and is therefore a measure of the time period within which the adhesive can be processed. Determination of tensile shear strengths The tensile shear strength was determined using a tensile testing machine (Shimadzu, AGS-X HC 20 KN) 48 hours after application (22°C, 40% rel. Humidity, test speed 1.3 mm / minute for metal and plastic substrates) according to DIN EN 1465:2009. The tensile strength values ​​given were determined as an average value, measured on three test specimens each. Production of a transparent 2-component structural adhesive (according to the invention) [Mixture of components i) and iii)] (NCO / NH = 1.71) 96 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 2500 mPas (23°C), Desmodur ultra N3300, a commercial product of Covestro AG, Leverkusen [component i)] are blended with 4 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] [Mixture of components ii) and iii)] 91 wt% polyether aspartic acid ester 4, Desmophen NH1723, commercial product of Covestro AG, Leverkusen [component ii)] are blended with 7 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 2 wt% demineralized water [component iii)] Example 2: Production of an opaque 2-component structural adhesive (according to the invention) Component A: [Mixture of components i) and iii)] (NCO / NH = 1.49) 62 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 2500 mPas (23°C), Desmodur ultra N3300, a commercial product of Covestro AG, Leverkusen [component i)] are blended with 3 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 35 wt.% of the filler talc 0, commercial product of Heinrich Heller GmbH, Leverkusen [component iii)] [Mixture of components ii) and iii)] 91 wt% polyether aspartic acid esters 3 [component ii)] are blended with 7 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 2 wt% demineralized water [component iii)] Example 3: Production of an opaque 2-component structural adhesive (according to the invention) Component A: [Mixture of components i) and iii)] (NCO / NH = 1.38) 72 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 20.0% and a viscosity of 16000 mPas(23°C), Desmodur ultra N3700, a commercial product of Covestro AG, Leverkusen [component i)] are blended with 2.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 25.5 wt% of the filler talc 0, commercial product of Heinrich Heller GmbH, Leverkusen [Component iii)] Component B: [Mixture of components ii) and iii)] 81 wt% polyether aspartic acid ester 4, Desmophen NH1723, commercial product of Covestro AG, Leverkusen [component ii)] are blended with 9 wt% of a cycloaliphatic polyaspartic acid ester, Desmophen NH1423, commercial product of Covestro AG, Leverkusen [component ii)] and 8.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 1.5 wt% demineralized water [component iii)] Example 4: Production of a transparent 2-component structural adhesive (according to the invention) Component A: [Mixture of components i) and iii)] (NCO / (NH+ROH) = 1.49) 95.5 wt% of a polyisocyanurate polyisocyanate based on Hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 2500 mPas (23°C), Desmodur ultra N3300, a commercial product of Covestro AG, Leverkusen [component i)], is blended with 4.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] Component B: [Mixture of components ii) and iii)] 88.55 wt.% polyether aspartic acid ester 4, Desmophen NH1723, commercial product of Covestro AG, Leverkusen [component ii)] are blended with 8.75 wt.% of a polydimethylsiloxane-functionalized highly dispersed pyrogenic silica, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 2.5 wt% 2,2',2"-Nitrilotriethanol [component ii)] and 0.2 wt% demineralized water [component iii)] Production of a transparent 2-component structural adhesive (according to the invention) [Mixture of components i) and iii)] (NCO / NH = 1.57) 5 97 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 20.0% and a viscosity of 16000 mPas(23°C), Desmodur ultra N3700, a commercial product of Covestro AG, Leverkusen [component i)] are blended with 3 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] [Mixture of components ii) and iii)] 91 wt% polyether aspartic acid ester 4, Desmophen NH1723, commercial product of Covestro AG, Leverkusen [component ii)] are blended with 9 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] Example 6: Production of an opaque 2-component structural adhesive (according to the invention) Component A: [Mixture of components i) and iii)] (NCO / NH = 1.63) 73 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 20.0% and a viscosity of 16000 mPas(23°C), Desmodur ultra N3700, a commercial product of Covestro AG, Leverkusen [component i)] are blended with 2 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 25 wt.% of the filler talc 0, commercial product of Heinrich Heller GmbH, Leverkusen [component iii)] Component B: [Mixture of components ii) and iii)] 60 wt% polyether aspartic acid ester 1 [component ii)] are blended with 30 wt% of a cycloaliphatic polyaspartic acid ester, Desmophen NH1423, commercial product of Covestro AG, Leverkusen [Component ii)] as well as 8.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen [component iii)] and 1.5 wt% demineralized water [component iii)] Comparison of adhesive properties The tensile shear strength was determined using a tensile testing machine as described above. Table: Comparison of adhesive bonding data Example 7: Non-inventive comparative example (analogous to EP 3 749 730 B1): Production of a transparent 2-component structural adhesive (non-inventive) Component A: (NCO / NH = 1.34) 96 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 2500 mPas (23°C), Desmodur Ultra N3300, a commercial product of Covestro AG, Leverkusen, is blended with 4 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, a commercial product of Evonik Industries AG, Essen Component B: 95 wt% linear aliphatic polyaspartic acid ester, Desmophen NH1220 (not derived from a polyether - therefore not according to the invention), a commercial product of Covestro AG, Leverkusen, are blended with 4.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, a commercial product of Evonik Industries AG, Essen and 0.5 wt.% demineralized water This adhesive has a pot life of 30 seconds at 23°C. The tensile shear strengths were determined for the following substrates: PMMA: 1.9 MPa PETG: 1.3 MPa This adhesive does not have sufficient adhesion to the substrates described. Example 8: Non-inventive comparative example (analogous to EP 3 749 730 B1): Production of an opaque 2-component structural adhesive (not according to the invention) Component A: (NCO / NH = 1.32) 76.5 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 2500 mPas(23°C), Desmodur ultra N3300, Trading products from Covestro AG, Leverkusen, are blended with 3.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, a commercial product of Evonik Industries AG, Essen and 20 wt% of the filler talc 0, commercial product of Heinrich Heller GmbH, Leverkusen Component B: 75.5 wt.% linear aliphatic polyaspartic acid ester, Desmophen NH1220, a commercial product of Covestro AG, Leverkusen, are blended with 4.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, a commercial product of Evonik Industries AG, Essen and 20 wt% of the filler talc 0, commercial product of Heinrich Heller GmbH, Leverkusen This adhesive has a pot life of 1 minute at 23°C. The tensile shear strengths were determined for the following substrates: PMMA: 1.6 MPa PETG: 2.6 MPa This adhesive does not have sufficient adhesion to the substrates described. Example 9: Non-inventive comparative example (analogous to WO 2021 / 023841 A1): Production of a transparent 2-component structural adhesive (not according to the invention) Component A: (NCO / NH = 1.51) 95.5 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 2500 mPas (23°C), Desmodur ultra N3300, a commercial product of Covestro AG, Leverkusen, is blended with 3.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, commercial product of Evonik Industries AG, Essen Component B: 95 wt% cycloaliphatic polyaspartic acid ester, Desmophen NH1423 (not derived from a polyether - therefore not according to the invention), a commercial product of Covestro AG, Leverkusen, are blended with 4.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, a commercial product of Evonik Industries AG, Essen and 0.5 wt.% demineralized water This adhesive has a pot life of 11 minutes at 23°C. The tensile shear strengths were determined for the following substrates: PMMA: 1.0 MPa PETG: 1.4 MPa This adhesive does not have sufficient adhesion to the substrates described. Example 10: Non-inventive comparative example (analogous to WO 2021 / 023841 A1): Production of an opaque 2-component structural adhesive (not according to the invention) Component A: (NCO / NH = 1.61) 76.5 wt% of a polyisocyanurate polyisocyanate based on hexamethylene diisocyanate with an NCO content of 21.8% and a viscosity of 2500 mPas (23°C), Desmodur ultra N3300, a commercial product of Covestro AG, Leverkusen, are blended with 3.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, a commercial product of Evonik Industries AG, Essen and 20 wt% of the filler talc 0, commercial product of Heinrich Heller GmbH, Leverkusen Component B: 65.5 wt.% cycloaliphatic polyaspartic acid ester, Desmophen NH1423, a commercial product of Covestro AG, Leverkusen, are blended with 4.5 wt% of a highly dispersed pyrogenic silica functionalized with polydimethylsiloxane, Aerosil R202, a commercial product of Evonik Industries AG, Essen and 30 wt% of the filler talc 0, commercial product of Heinrich Heller GmbH, Leverkusen This adhesive has a pot life of 7 minutes at 23°C. The tensile shear strengths were determined for the following substrates: PMMA: 1.6 MPa PETG: 1.6 MPa This adhesive does not have sufficient adhesion to the substrates described.

Claims

AMENDED CLAIMS received by the International Bureau on 26 November 2025 (26.11.2025) 1. Formulation for a 2-component structural adhesive for structural bonding of identical or different substrates, wherein this formulation contains at least: i) at least one polyisocyanate having free isocyanate groups and an aliphatic NCO group content of 16.0 to 24.0 wt.%, ii) at least one amino-functional polyaspartic acid ester of the general formula where R 1 and R 2 independently of each other, representing a methyl or an ethyl group; and where X represents a divalent organic residue obtained by removing the amino groups from aminopolyether of the general structural formula and isomers thereof, where n is a number in the range of 2 to 8, as well as; Hi) optionally at least one filler, auxiliary or additive, AMENDED SHEET (ARTICLE 19) characterized in that said formulation, after mixing all components and after curing, i.e. after at least 24 hours after mixing and application, has a tensile shear strength of at least 7 MPa according to DIN EN 1465 version 2009-07, as measured between two test specimens on roughened V2A steel.

2. Formulation according to claim 1, characterized in that n represents a number from 2.5 to 6.5, or that n represents a number from 2.5 to 4.

5.

3. Formulation according to claim 1 or claim 2, characterized in that R 1 and R 2each representing an ethyl group, and / or that in the structural formula for the aminopolyether according to claim 1, or in a preferred embodiment of the structural formula for the aminopolyether according to claim 1, X represents a divalent organic residue obtained by removing the amino groups from aminopolyether, wherein the aminopolyether contains 9 to 27 carbon atoms and 2 to 8 oxygen atoms.

4. Formulation according to one or more of claims 1 to 3 comprising i) at least one polyisocyanate based on hexamethylene diisocyanate having free isocyanate groups and a content of aliphatically bound NCO groups of 19.0 to 23 wt.%. AMENDED SHEET (ARTICLE 19) 5. Formulation according to one or more of claims 1 to 4, characterized in that said formulation, after mixing all components and before application to a substrate, has a viscosity at 23°C according to DIN EN 12092:2001 in the version of February 2002 in the range of 1000 mPa s to 400,000 mPa s, preferably from 2000 mPa s to 200,000 mPa s, more preferably from 5000 mPa s to 200,000 mPa s.

6. Formulation according to one or more of claims 1 to 5, characterized in that said formulation, after mixing all components, has a pot life according to DIN EN ISO 10364:2024 (April 2024) of 5 min to 100 min, preferably of 10 min to 75 min.

7. Formulation according to one or more of claims 1 to 6, characterized in that said formulation, after mixing all components and after curing, i.e. after at least 24 hours after mixing and application, has a tensile shear strength according to DIN EN 1465 Version 2009-07 of at least 10 MPa, as measured between two test specimens on roughened V2A steel.

8. Formulation according to one or more of claims 1 to 7, characterized in that this formulation is present in a mixture with at least one other isocyanate-reactive substance, wherein the following applies: • the amino-functional polyaspartic acid ester based on aminopolyethers as defined above, and at least one other isocyanate-reactive substance, are both present together as a mixture in component ii), and AMENDED SHEET (ARTICLE 19) • wherein at least 10 wt %, preferably at least 20 wt %, further preferably at least 40 wt %, further preferably at least 60 wt %, of the total mixture in component ii) are polyaspartic acid esters based on aminopolyethers as defined in one of the preceding claims.

9. Formulation according to claim 8, wherein the at least one other polyaspartic acid ester is a polyaspartic acid ester of the general formula according to claim 1, wherein X represents a divalent organic residue obtainable by removing the amino groups from diamino-dicyclohexylmethane or a straight-chain or branched aliphatic diamine, which preferably has up to 9 carbon atoms, wherein polyaspartic acid esters based on 2-methyl-1,5-diaminopentane and diethyl maleate and diamino-dicyclohexylmethane and diethyl maleate are particularly preferred.

10. Formulation according to one or more of claims 1 to 9, characterized in that component iii) contains water, preferably in amounts of 0.05 wt.% to 1 wt.%, based on the total weight of the formulation.

11. Formulation according to one or more of claims 1 to 10, characterized in that the two components i) and ii) are used in a volume ratio of 60:40 to 40:60, wherein components i) and ii) optionally each contain component iii), or that the two components i) and ii) are used in a volume ratio of 50:50, wherein components i) and ii) optionally each contain component iii). AMENDED SHEET (ARTICLE 19) 12. Use of the formulation according to one or more of claims 1 to 11 for the structural bonding of at least two substrates, preferably of at least two substrates containing engineering plastics.

13. Method for structurally bonding at least two substrates, wherein the method comprises at least the following steps: (a) Providing a formulation for a 2-component structural adhesive according to one or more of claims 1 to 11; (b) Application of the formulation from (a) to at least one substrate; (c) Bonding of at least two substrates, one of which is the substrate from (b).

14. System comprehensive: (1) at least two substrates joined together by a cured 2-component structural adhesive, wherein the 2-component structural adhesive comprises a cured formulation according to any one of claims 1 to 11. (2) said cured 2-component structural adhesive.

15. System according to claim 14, wherein the 2-component structural adhesive in the system has a tensile shear strength according to DIN EN 1465 version 2009-07 of at least 7 MPa, preferably at least 10 MPa, as measured between two test specimens on roughened V2A steel, and / or wherein the gap dimension, i.e. the thickness of the structural adhesive layer between the two substrates, ranges from 1 pm to 1 cm, preferably from 50 pm to 2 mm. AMENDED SHEET (ARTICLE 19)

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