Method for producing recyclable single-material multi-layer system

Abstract

The invention relates to a method for producing a single-material multilayer system, in particular a recyclable single-material multilayer system, said method comprising or consisting of the following steps: I) providing at least two single-material layers; iI) indirectly or directly applying a two-component adhesive to at least one of the provided two single material layers, the two-component adhesive comprising at least one isocyanate-reactive component and at least one isocyanate component; iII) joining the single material layers by means of a two-component adhesive and curing the two-component adhesive to obtain a single material multilayer system; the invention relates to a single-material multilayer system, characterized in that the material of the single-material layer comprises a polyolefin and the proportion of the polyolefin is 80.0 to 99.30% by weight, based on the total weight of the single-material multilayer system, the proportion of the two-component binder is 0.70 to 20.0% by weight, based on the total weight of the single-material multilayer system, the isocyanate reactive component and / or the isocyanate component comprises "CH2-O-" n units, and the cured two-component adhesive has a ratio of "CH2-O-" n units of 7.0 to 25.0 wt%, based on the total weight of the adhesive, where n is a number from 2 to 50.

Description

[0001] This invention relates to a method for preparing a single-material multilayer system, particularly a recyclable single-material multilayer system, the single-material multilayer system obtained or obtainable by this method, and the use of a single-material multilayer system. Furthermore, this invention relates to the use of two-component adhesives in single-material multilayer systems, particularly for improving their recyclability. Finally, this invention relates to a method for obtaining recyclables from waste containing a single-material multilayer system, the waste comprising the single-material multilayer system according to the invention, and molded parts obtained or obtainable by processing the recyclables obtained or obtainable according to the above-described recycling method. Background Technology

[0002] Packaging made from film composites (multilayer systems) is frequently used for industrial and consumer product packaging. These film composites consist of film layers with different properties. Such composites can be prepared, for example, by lamination with an adhesive or by extrusion, optionally using an intermediate layer as an adhesive layer (binding layer). For example, such multilayer film composites contain polyolefin, polyester, and aluminum film layers. The properties required for use as packaging materials, such as mechanical strength, sealing, and barrier properties, can be achieved through combinations of various materials with very specific properties. Unfortunately, due to the different material properties, these composites cannot be processed into high-quality recyclables in the sense of mechanical recycling. However, recycling is an interesting way to conserve resources and reduce environmental impact. For the reasons mentioned above, as well as cost considerations and regulatory requirements, more and more companies are seeking to reduce emissions, which is why the concept of recycling is also desirable. Therefore, industry is looking for ways to improve the quality of recyclables generated from packaging machinery recycling so that they can be increasingly used in film production.

[0003] Recently, so-called single-material packaging systems consisting of single-material layer systems have been proposed, which are particularly suitable for mechanical recycling after use. These are typically prepared by extrusion lamination or by laminating two layers of polyolefin film with an adhesive, particularly by lamination with a two-component (2K) polyurethane adhesive. The latter has the advantage of being able to use a wider range of materials, such as pre-coated film layers. In the case of so-called single-material packaging, film layers with different properties are also combined with each other; however, these film layers are mainly composed of materials of the same material class, such as polyolefins. Different properties of the corresponding film layers can be obtained by selecting different base polymers, additives, pretreatments, and especially coatings.

[0004] However, it has been found that the recyclables obtained during the mechanical recycling of such packaging, which consists of a single-layer material system, are unsuitable or only suitable to a limited extent for the preparation of high-quality films or other molded parts, and, if any, can only be added in small amounts during the preparation of new polyolefin films from so-called virgin materials. A common problem is that new films prepared using recyclables have optical defects and / or poorer mechanical properties (e.g., elongation at break, modulus) compared to films prepared from “virgin” materials, due to the 2K polyurethane adhesive commonly used for laminating films, whose cured form is incompatible with polyolefins, and whose use is increasingly criticized. The use of this adhesive is limited to low weight contents within the product specifications of recyclable packaging, and alternatives are being sought.

[0005] CN 110861380 A describes a recyclable packaging using a polyurethane adhesive with barrier properties. The content of the solvent-free polyurethane adhesive, not described in detail in the composite material, is limited to less than 1%. No mention is made of the adhesive's impact on the quality of the resulting recyclables. The use of the adhesive raw material based on renewable resources is not described.

[0006] WO 2019 / 209337 A1 describes a multilayer composite film with increased recyclability prepared using polylactide as an intermediate layer. Polylactide can be prepared based on renewable raw materials. The use of polyolefins as film layers is not explicitly described.

[0007] WO 2021 / 069668 A1 describes recyclable packaging based on polyethylene, mentioning the possible use of solvent-free or solvent-based adhesives based on polyurethane, but does not discuss the exact composition of the adhesives. The impact of the adhesives on the quality of the recycled materials is not discussed.

[0008] WO 2019 / 027527 A1 describes a polyethylene-based recyclable packaging using a solvent-based polyurethane adhesive with barrier properties. The impact of the adhesive on the quality of the recycled material is not discussed. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide a method for preparing a single-material multilayer system that is recyclable and yields a recyclable material of good quality, particularly good homogeneity, upon recycling. Furthermore, the adhesive should be particularly used in the preparation of the single-material multilayer system, which may be prepared at least partially from bio-based raw materials and optionally results in good composite strength of the single-material multilayer system.

[0010] Solutions and detailed instructions

[0011] This objective is achieved by the method described in claim 1.

[0012] In the course of the development work leading to this invention, it was surprisingly discovered that the use of a specific two-component binder in the preparation of monomaterial multilayer systems, which mainly comprise polyolefins (based on 80.0 to 99.30% by weight of the total weight of the monomaterial multilayer system), results in recyclable monomaterial multilayer systems with particularly high composite strength. When these monomaterial multilayer systems are recycled, recyclables of improved quality are obtained, particularly exhibiting good homogeneity. Therefore, due to their good quality, the recyclables are suitable for further processing, particularly for the production of molded parts.

[0013] In the context of this invention, the terms "recyclable" or "recyclability" are understood to mean the suitability of a single-material multilayer system to be processed into a recyclable with high homogeneity by mechanical recycling methods, even if the single-material multilayer system has a proportion of a two-component binder of >1.0 wt% based on the total weight of the single-material multilayer system. The homogeneity of the recyclable is determined by compounding the single-material multilayer system at high temperature in an extruder and by pressing a film with a thickness of 200 µm from the extrudate. The film is optically examined using an optical microscope, and, if necessary, its non-uniformity is examined with the support of an evaluation procedure. A recyclable with high or good homogeneity is characterized by a uniformity of approximately 1.1 cm², as determined by microscopic examination (optical microscope). 2 The number of defects on the inspected surface is <3000, preferably <2000, and particularly preferably <1500. Regarding the total area of ​​defects, if the total area of ​​defects in the pressed film produced from the recycled material is less than 3%, preferably less than 2.5%, then a homogeneous recycled material exists. In contrast, the homogeneity of films prepared from extrudates obtained by compounding a predetermined amount of pulverized cured adhesive with a specified amount of other components of a single-material layer system (or: "the single-material layer used") at high temperature in an extruder and then pressing the film from the extrudate. This method is particularly suitable for determining the maximum adhesive content that still yields a recyclable single-material layer system.

[0014] According to the present invention, the composite strength of a single-material multilayer system is determined in a 180° peel test (180° peel strength), wherein the composite film is cut into strips 15 mm wide. The strips are then peeled at 100 mm / min at an angle of 2 × 90° (180°) at 23°C using a Zwick peel strength universal tester (model 5kNAllround Table-top BT2-FA005TH.A50.002), and the required force is measured in Newtons. Sufficient composite strength is given when a value of at least 0.5 N / 15 mm is achieved.

[0015] According to the present invention, a single-material multilayer system is understood to be a layer system made of at least two single-material layers and a two-component adhesive. Preparation includes or comprises the following steps: I) Provide at least two single-material layers; II) Applying a two-component adhesive, either indirectly or directly, to at least one of the two provided single-material layers, wherein the two-component adhesive comprises at least one isocyanate reactive component and at least one isocyanate component; III) Connect single-material layers with a two-component adhesive and cure the two-component adhesive to obtain a single-material multilayer system.

[0016] The material of the monomaterial layer comprises a polyolefin, wherein the proportion of the polyolefin is 80.0 to 99.30% by weight, preferably 95.0 to 98.0% by weight, based on the total weight of the monomaterial multilayer system. These are preferably polyolefin films, which may also be coated. The monomaterial layer may also contain additives known to those skilled in the art, particularly anti-blocking agents, dyes, pigments, and stabilizers. The monomaterial layer, such as a polyolefin film, can be prepared by various methods known to those skilled in the art, such as by extrusion of blown film. By these methods, monomaterial layers with multiple layers of different or identical compositions can be obtained. To establish the desired properties, the monomaterial layer may optionally be axially or biaxially stretched and / or coated at a temperature below the melting temperature. In particular, a barrier layer may be applied, for example, consisting of silica, alumina, EVOH, PVOH, or acrylate and / or printing inks and / or primers.

[0017] The melting points of the at least two monomaterial layers preferably differ by 5 to 90 K, more preferably 10 to 20 K. Furthermore, one of the at least two monomaterial layers preferably has a melting point of 100 to 115 °C, more preferably 100 to 105 °C, while the other layer has a melting point of 140 to 170 °C, more preferably 140 to 155 °C. If the sealing layer is present on at least one side of the monomaterial multilayer system, the monomaterial multilayer system can also be prepared using polyolefins having the same or nearly the same melting points. Melting point and melting temperature are used synonymously here. The melting temperature is determined by DSC (differential scanning calometry) at a heating rate of 20 K / min according to DIN EN ISO 11357-1:2017 (2017-02) and standard part 11357-2.

[0018] The preferred single-layer polyolefin is selected from the group consisting of or composed of polyethylene, polypropylene, or mixtures thereof. The polyolefin can be prepared, for example, by chain polymerization of olefins such as ethylene, propylene, 1-butene, and / or isobutene. In the preparation of the polyolefin, ethylene and / or propylene are preferably used as monomers.

[0019] Preferably, a single-material layer composed primarily of polypropylene (e.g., BOPP (biaxially oriented polypropylene)) and / or polyethylene (e.g., BOPE (biaxially oriented polyethylene)) is used. A single-material layer composed of polyethylene, particularly BOPE (biaxially oriented polyethylenylene), is very particularly preferred. Preferably, the single-material layer system consists of two single-material layers primarily composed of polyethylene or two single-material layers primarily composed of polypropylene. In another preferred embodiment, the single-material layer system in each case consists of a single-material layer primarily composed of polyethylene and a single-material layer primarily composed of polypropylene.

[0020] The two-component adhesive comprises at least one isocyanate reactive component and at least one isocyanate component. The two-component adhesive is also referred to below as 2K adhesive or 2K polyurethane adhesive. The proportion of the two-component adhesive is 0.70 to 20.0% by weight, preferably 0.70 to 10.0% by weight, more preferably 1.0 to 5.0% by weight, based on the total weight of the single-material multilayer system. The two-component adhesive preferably also contains organic solvents, catalysts, fillers, processing aids, adhesion promoters, especially silanes, stabilizers, especially antioxidants, or mixtures thereof. It is also preferred that the stoichiometric ratio of the isocyanate groups to the isocyanate reactive groups of the two-component adhesive is between 0.8:1 and 2:1, preferably between 1.1:1 and 1.5:1, particularly preferably between 1.1:1 and 1.4, and very particularly preferably between 1.1 and 1.2. The components of the two-component adhesive are preferably mixed or otherwise brought into close contact before application to the substrate. Optionally, one or two monomaterial layers in indirect or direct contact with the adhesive may be corona pretreated to increase surface energy before applying the adhesive and / or contacting the applied adhesive layer.

[0021] The preparation of 2K polyurethane adhesives is generally known to those skilled in the art. Ulrich Meier-Westhues, Polyurethane-Lacke, Kleb-und Dichtstoffe, and Hannover provide chemical structures and formulations, as well as processing methods, particularly in the case of 2K polyurethane adhesives for the preparation of composite films or multilayer composite films: Vincenz Network 2007, Chapter 6, e.g., pp. 247-253.

[0022] Unless otherwise stated, the average functionality of a compound should be understood as the average number of isocyanate functional groups or isocyanate groups per molecule. For compounds with undefined or homogeneous compositions, such as oligomers or polymers, those skilled in the art can determine the average functionality using various methods. For example, the average functionality can be calculated from the isocyanate content and the number-average molecular weight, which is determined, for example, by gel permeation chromatography (GPC) or vapor pressure permeation. A similar procedure can be performed for isocyanate-reactive compounds. For example, the average OH functionality of a compound can be calculated based on the number-average molecular weight and the number of hydroxyl groups. Unless otherwise stated, the number of hydroxyl groups (OH number) of a compound is determined according to DIN EN ISO 4629-2, wherein N-methylpyrroledione is substituted with pyridine.

[0023] The isocyanate reactive component and / or isocyanate component of the two-component adhesive contain [CH2-O-]. n The unit, and the cured two-component adhesive has 7.0 to 25.0% by weight of [CH2-O-] based on the total weight of the adhesive. n The proportion of units, where n is a number from 2 to 50, preferably 8 to 20. In this case, the isocyanate reactive component or isocyanate component preferably has an average molecular weight Mn of <1000 g / mol and an average functionality of >2 (also called "crosslinking agent component"), and in each case, the other component has an average molecular weight Mn of >1000 g / mol and a functionality of <4 (also called "prepolymer component"). In other words, the isocyanate reactive component is preferably a crosslinking agent component and the isocyanate component is preferably a prepolymer component, or the isocyanate reactive component is preferably a prepolymer component and the isocyanate component is preferably a crosslinking agent component. The prepolymer component can also be used for both components, but it is less preferred because the increase in molecular weight is generally not very rapid, and the increase in composite strength is delayed. This leads to problems in the preparation of composite films, such as the known phenomenon of the film roll "stretching" under tensile stress during winding.

[0024] Unless otherwise stated, the number-average molecular weight Mn and weight-average molecular weight Mw are determined according to DIN 55672-1 "Gel permeation chromatography, Part 1 - Tetrahydrofurans as eluents".

[0025] In the context of this invention, "isocyanate reactive group" refers to a functional group capable of reacting with an isocyanate group (-N=C=O) at temperatures up to 200°C to form at least one covalent bond. Isocyanate reactive compounds are, for example, compounds having an active hydrogen atom. Examples of such compounds are water, alcohols, primary and secondary amines, thiols, and carboxylic acids. Compounds that do not contain an active hydrogen atom but still react with isocyanates are, for example, epoxides, oximes, carbon dioxide, and carboxylic anhydrides. Suitable reactive functional groups can be monofunctional groups that react with isocyanates, such as OH groups or mercapto groups. However, they can also be difunctional groups of isocyanates, such as amino groups. Thus, a molecule having an amino group also has two functional groups that react with isocyanate groups. In this case, it is not necessary for a single molecule to have two independent functional groups that react with isocyanate groups—it is important that the molecule is capable of forming compounds with two isocyanate groups, forming covalent bonds in each case. Examples of structural features arising from the reaction of isocyanate groups with isocyanate reactive compounds include ethyl carbamate, alloalkyl esters, biuret, urea, thiocarbamate, amides, imides, acylureas, oxazolidinones, carbamates, and oxadiazine triones. Examples of structural features formed by the reaction of at least two isocyanate groups include urea dione, isocyanurate, and carbodiimide. Catalysts are commonly used to form these groups. Examples of suitable catalysts are given in Chapter XII, Overview of Catalytic Effects, Polymers, Volume XVI, Polyurethanes: Chemistry and Technology, Part I, Chemistry JH Saunders and KC Frisch, John Wiley & Sons (Library of Congress Catalogue Card No. 62-18932).

[0026] The preferred two-component adhesive's isocyanate reactive component comprises or consists of polyols, particularly polyester polyols, polyether polyols, hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, hydroxyl-containing reaction products of hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, and diisocyanates or mixtures of the above compounds. Polyols are understood as polyfunctional alcohols, i.e., compounds containing one or more OH groups in their molecules.

[0027] If the isocyanate reactive component contains [CH2-O-] nThese units are preferably polyols with an OH functionality between 1 and 4 and an OH value between 5 mg KOH / g and 900 mg KOH / g, such as, in particular, hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers. Such polyols can be obtained through various means known to those skilled in the art: for example, WO 2004 / 096746 A1 experimentally describes isocyanate-reactive diols based on polyoxymethylene (POM) with OH values ​​of 685 and 868 mg KOH / g, which can be reacted with polyisocyanates to yield isocyanate-reactive groups with lower OH values. According to EP 3 922 661A1, further possible starting compounds can be prepared by reacting polyoxymethylene compounds with alkylene oxides and polyols in the presence of a dimetallic cyanide (DMC) catalyst. US 3754053 describes polyoxymethylene-polyoxyalkylene copolymers with molecular weights >10,000 g / mol, starting from trioxanes. WO2021122402A1 teaches the preparation of polyoxymethylene-polyoxyalkylene copolymers, comprising reacting a polyoxymethylene compound with an alkylene oxide in the presence of a bimetallic cyanide (DMC) catalyst, wherein the polyoxymethylene compound has at least one terminal hydroxyl group, and wherein the method comprises the steps of: first introducing a suspending agent into a reactor, and then metering the polyoxymethylene compound into the reactor stepwise or continuously during the reaction. Other possible starting compounds are described in WO2015 / 155094A1, WO2012 / 091968, EP 1870425A1, and JP 2007211082. It is also preferred to use compounds containing urethane groups and [CH2-O-] with a molecular weight Mw > 1000 to 30,000. n Polyols containing [CH2-O-]n units. These can be obtained, for example, by reacting diisocyanates with polyols containing [CH2-O-]n units, using an excess of hydroxyl groups relative to the isocyanate group. Particularly preferred diisocyanates used in this reaction are 1,5-pentane diisocyanate (PDI), 1,6-hexane diisocyanate (HDI), 1-isocyanate-3,3,5-trimethyl-5-isocyanate methylcyclohexane (isophorone diisocyanate, IPDI), 2,4'- and 4,4'-diisocyanate diphenylmethane (MDI), and 2,4- and 2,6-diisocyanate toluene (TDI). The stoichiometric ratio of the isocyanate group to the hydroxyl group is preferably between 1:10 and 9.5:10.

[0028] The isocyanate reactive component may contain only one polyol, but a mixture of two or more polyols may also be used as the polyol component. Furthermore, components containing [CH2-O-] may also be used. n A mixture of polyols containing [CH2-O-] units may also be used, if appropriate. nOther compounds with isocyanate reactive groups of the unit.

[0029] In a particular embodiment of the invention, the isocyanate reactive component is water (H2O), or the isocyanate reactive component contains water. Although a water molecule contains only one hydroxyl group, it can react with two NCO groups because, after reacting with the isocyanate groups and eliminating carbon dioxide, an amine group is formed, which in turn can react with one or more other isocyanate groups. Therefore, in a particular embodiment, the isocyanate reactive component is not mixed with component B before the adhesive is applied, but rather occurs, for example, after the two substrates are joined by a substrate having corresponding water vapor permeability, as atmospheric moisture through diffusion.

[0030] The method according to the invention uses [CH2-O-] n The compounds of the unit are preferably polyoxymethylene-polyoxyalkylene copolymers and their derived prepolymers and other derivatives. In the context of this invention, polyoxymethylene-polyoxyalkylene copolymers refer to polymer compounds containing at least one polyoxymethylene block and at least one additional polyoxyalkylene block, and preferably with a molecular weight not exceeding four digits. As described on page 5, line 28 to page 13, line 3 of WO2022049012 A1, polyoxymethylene-polyoxyalkylene copolymers used in the novel method are prepared by catalytic addition of alkylene oxides and optionally other comonomers to at least one polyoxymethylene initiator compound having at least one terminal hydroxyl group in the presence of a bimetallic cyanide (DMC) catalyst. Polyoxymethylene-polyoxyalkylene copolymers with hydroxyl values ​​of 5 mg KOH / g to 200 mg KOH / g and an average functionality of 1.6 to 4, according to DIN EN ISO 4629-2, are particularly preferred as components of the isocyanate reactive component itself or as synthetic components of compounds used in isocyanate reactive components and / or isocyanate components, and contain [CH2-O-]. n The unit is a polyol.

[0031] Regarding the isocyanate component of the two-component adhesive, the preferred... The monomeric polyisocyanate composition, particularly hexamethylene-1,6-diisocyanate, pentamethylene-1,5-diisocyanate, 1,4-butane diisocyanate, isophorone diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-2,2'-diisocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, or mixtures thereof; Composed of oligomeric polyisocyanates prepared from at least two monomeric polyisocyanates; The isocyanate-terminated prepolymer composition is prepared by reacting monomers and / or oligomeric polyisocyanates with isocyanate reactive compounds having >1 isocyanate reactive group per molecule, wherein the isocyanate reactive compound preferably comprises or is composed of polyols, more preferably hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, polyacrylates, polycarbonates, polyesters, polyurethanes and / or polyethers. Or a mixture of the above compounds The isocyanate-terminated prepolymer preferably has the [CH2-O-] structure as described above. n unit.

[0032] If the isocyanate component has [CH2-O-] n The unit is preferably prepared by methods known to those skilled in the art, for example by using [CH2-O-] n The unit can also be used in the isocyanate reactive component of two-component adhesives to react with excess polyisocyanate to obtain compounds with [CH2-O-]. n Isocyanate-terminated compounds of the unit. For example, isocyanate-terminated prepolymers prepared based on polyoxymethylene-polyoxyalkylene copolymers (e.g., described in EP 3960783A1) can be used as the isocyanate component. The use of amino-containing polyethers is possible but not mandatory. Furthermore, isocyanate-reactive diols based on polyoxymethylene (POM), such as those with OH values ​​of 685 and 868 mg KOH / g, as described in WO 2004 / 096746 A1, can be used, which can be reacted with polyisocyanates to yield compounds containing isocyanate groups. NCO-modified polyoxymethylene copolymers disclosed in WO 2014 / 095679 can also be used. All reactive compounds comprising isocyanate reactive compounds of two-component binders may contain [CH2-O-]. n Units, or those containing [CH2-O-]. n In addition to reactive compounds, the unit may also contain or not contain [CH2-O-]. n Compounds containing [CH2-O-]. However, if the isocyanate reactive compound contains [CH2-O-]... n For compounds containing only [CH2-O-] units, isocyanate reactive compounds can also be formed solely by compounds that do not contain [CH2-O-]. n The unit is composed of reactive compounds.

[0033] The term "polyisocyanate" as used herein is a general term for compounds whose molecules contain two or more isocyanate groups (which those skilled in the art understand as free isocyanate groups of the general formula -N=C=O). The simplest and most important representative of these polyisocyanates is the diisocyanate. It has the general structure O=C=NRN=C=O, where R usually represents an aliphatic, alicyclic, and / or aromatic free radical.

[0034] Therefore, in this application, the term "polyisocyanate" refers to both monomers and oligomeric polyisocyanates. When "oligomeric polyisocyanate" is mentioned in this application, it refers to a polyisocyanate composed of at least two monomeric polyisocyanate molecules, that is, a compound representing or containing the reaction product of at least two monomeric polyisocyanate molecules. Preferably, the monomeric polyisocyanate is a diisocyanate, i.e., a monomeric isocyanate having two isocyanate groups per molecule. Unlike isocyanate-terminated prepolymers further defined below in this application, oligomeric polyisocyanates are characterized by a molecular weight of not more than 900 g / mol, preferably not more than 800 g / mol, and particularly preferably not more than 700 g / mol.

[0035] According to the present invention, oligomeric polyisocyanates may particularly have structures of urea diketone, isocyanurate, alloalkylate, biuret, iminooxadiazine diketone, and / or oxadiazine triketone. According to one embodiment of the present invention, the oligomeric polyisocyanate has at least one of the following oligomeric structural types or mixtures thereof:

[0036] The methods for preparing oligomeric polyisocyanates having structures of urea diketone, isocyanurate, alloalkylate, biuret, iminooxadiazine diketone, and / or oxadiazine triketone used in this invention are described, for example, in J. Prakt. Chem. 336 (1994) 185-200, in DE-A 1 670 666, DE-A 1 954 093, DE-A 2 414 413, DE-A 2 452 532, DE-A 2 641 380, DE-A 3 700 209, DE-A 3 900 053 and DE-A 3 928 503 or EP-A 0 336 205, EP A 0 339 396 and EP-A 0 798 299.

[0037] In isocyanates having aliphatic bonded isocyanate groups, all isocyanate groups are bonded to sp3 hybrid carbon atoms. Preferred polyisocyanates having aliphatic bonded isocyanate groups are n-butyl isocyanate and all its isomers, n-pentyl isocyanate and all its isomers, n-hexyl isocyanate and all its isomers, 1,4-butyl diisocyanate, 1,5-diisocyanate pentane (PDI), 1,6-diisocyanate hexane (HDI), 2-methyl-1,5-diisocyanate pentane, 1,5-diisocyanate-2,2-dimethylpentane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanate hexane, 1,10-diisocyanate decane, and nonane triisocyanate.

[0038] In isocyanates with aliphatic ring-bonded isocyanate groups, all isocyanate groups are bonded to carbon atoms, which are part of a closed carbon ring. This ring can be unsaturated at one or more positions, provided it does not possess aromatic properties due to the presence of double bonds. Preferred polyisocyanates having aliphatic ring-bonded isocyanate groups are cyclohexyl isocyanate, 1,3- and 1,4-diisocyanate cyclohexane, 1,4-diisocyanate-3,3,5-trimethylcyclohexane, 1,3-diisocyanate-2-methylcyclohexane, 1,3-diisocyanate-4-methylcyclohexane, 1-isocyanate-3,3,5-trimethyl-5-isocyanate methyl-cyclohexane isophorone diisocyanate (IPDI), 1-isocyanate-1-methyl-4(3)-isocyanate methylcyclohexane, 2,4'- and 4,4'-diisocyanate dicyclohexylmethane (H12MDI), 1,3- and 1, 4-Bis(isocyanate methyl)cyclohexane, bis(isocyanate methyl)-norbornene (NBDI), 4,4'-diisocyanate-3,3'-dimethyldicyclohexylmethane, 4,4'-diisocyanate-3,3',5,5'-tetramethyl-dicyclohexylmethane, 4,4'-diisocyanate-1,1'-bis(cyclohexyl), 4,4'-diisocyanate-3,3'-dimethyl-1,1'-bis(cyclohexyl), 4,4'-diisocyanate-2,2',5,5'-tetramethyl-1,1'-bis(cyclohexyl), 1,8-diisocyanate-p-menthane, 1,3-diisocyanate-adamantane, and 1,3-dimethyl-5,7-diisocyanate-adamantane.

[0039] In isocyanates having aromatically bonded isocyanate groups, all isocyanate groups are bonded to alkylene groups, which in turn are bonded to aromatic rings. Preferred polyisocyanates having aromatically bonded isocyanate groups are 1,3- and 1,4-bis(methyl isocyanate)benzene (xylene diisocyanate; XDI), 1,3- and 1,4-bis(1-methylethyl isocyanate)benzene (TMXDI), and bis(4-(1-methylethyl isocyanate)phenyl)carbonate.

[0040] In isocyanates having aromatically bonded isocyanate groups, all isocyanate groups are directly bonded to carbon atoms that are part of the aromatic ring. Preferred isocyanates having aromatically bonded isocyanate groups are toluene 2,4- and 2,6-diisocyanate (TDI), diphenylmethane 2,4'- and 4,4'-diisocyanate (MDI), naphthalene 1,5-diisocyanate, tris(phenyl)thiophosphate, and triphenylmethane-4,4',4''-triisocyanate.

[0041] The isocyanate-terminated prepolymer is obtained by reacting a monomer or oligomeric polyisocyanate with a compound containing, on average, more than one isocyanate reactive group per molecule, wherein the reaction mixture contains an isocyanate group in molar excess relative to the isocyanate reactive group. The compound containing, on average, more than one isocyanate reactive group per molecule is preferably a polyol and / or a polyamine, wherein the isocyanate group in the reaction mixture is in molar excess relative to the amino and hydroxyl groups. The corresponding preparation methods are well known to those skilled in the art.

[0042] The 2K polyurethane adhesive used according to the present invention can be largely prepared from renewable raw materials (biomethanol). In this case, for example, diisocyanates having a bio-based carbon moiety are used, such as pentamethylene diisocyanate prepared from bio-based cadaverine, hexamethylene diisocyanate based on bio-based hexamethylenediamine, methylene diisocyanate prepared from bio-based aniline, and / or isophorone diisocyanate prepared from bio-based acetone, or derivatives, oligomers, and / or prepolymers synthesized from these compounds.

[0043] The corresponding diamine can be obtained through enzymatic conversion, for example, from sugar or starch compounds.

[0044] Furthermore, it is preferable to use [CH2-O-] prepared from formaldehyde derived from bio-methanol. n unit.

[0045] The present invention also relates to the use of the two-component adhesive according to the invention in a single-material multilayer system, particularly for improving the recyclability of the single-material multilayer system, wherein the material of the single-material layer comprises 80.0 to 99.3% by weight of polyolefin relative to the total weight of the single-material multilayer system.

[0046] The present invention also relates to single-material multilayer systems, particularly recyclable single-material multilayer systems, obtained or obtainable by the method according to the invention. In this case, the single-material multilayer system according to the invention can be used particularly as packaging material, preferably recyclable packaging material, especially food packaging material.

[0047] Since the single-material multilayer system according to the invention is suitable for preparing high-quality recyclables, the invention also relates to a method for obtaining recyclables from waste containing a single-material multilayer system according to the invention, wherein the method comprises the following steps: i. Grinding, washing, and optionally sterilizing waste containing a single-material multilayer system to obtain a mixture of materials; ii. Optionally classify the mixture of materials; iii. Optionally, the material mixture may be mixed with other components, particularly with polyolefins; iv. Further processing, particularly melting and extruding the material mixture, to obtain recyclables.

[0048] Therefore, this method is a mechanical recycling method. In addition to the single-material multilayer system according to the invention, non-inventory single-material multilayer systems, particularly recyclable single-material multilayer systems, as well as other additives (other components), such as synthetically prepared or unreused PE or PO particles (so-called "virgin" materials or "virgin polyolefins"), can also be used.

[0049] Therefore, in the sense of this invention, recycled material refers to the product obtained at least after crushing and washing waste containing a single-material multilayer system and further processing. Further processing preferably includes an extrusion process, whereby the recycled material can be obtained, for example, in granule or strand form. The recycled material comprises at least one polyolefin and at least one cured form of 2K polyurethane adhesive.

[0050] For example, after melting and extrusion, especially when the cured two-component adhesive contains 7.0 to 25.0% by weight of [CH2-O-]. n The unit, preferably 9.0 to 20.0% by weight of [CH2-O-] n The unit, preferably 15.0 to 18.0% by weight of [CH2-O-], is preferred. n In a unit, a uniform amount of recyclable material is produced.

[0051] The recycled materials according to the invention can be used to prepare films or other molded parts, optionally with the addition of (further) virgin polyolefins. Therefore, the invention also relates to molded parts and films obtained or available by processing recycled materials obtained or available through the recycling method according to the invention.

[0052] Implementation method: This invention particularly relates to the following embodiments: According to a first embodiment, the present invention relates to a method for preparing a single-material multilayer system, particularly a recyclable single-material multilayer system, wherein the method includes or comprises the following steps: I) Provide at least two single-material layers; II) Applying a two-component adhesive, either indirectly or directly, to at least one of the two provided single-material layers, wherein the two-component adhesive comprises at least one isocyanate reactive component and at least one isocyanate component; III) Connect single-material layers with a two-component adhesive and cure the two-component adhesive to obtain a single-material multilayer system; The feature is that the material of the single-material layer comprises a polyolefin, and the proportion of the polyolefin is 80.0 to 99.30% by weight based on the total weight of the single-material multilayer system. The proportion of the two-component adhesive is 0.70% to 20.0% by weight based on the total weight of the single-material multilayer system. The isocyanate reactive component and / or isocyanate component contains [CH2-O-]. n unit, and The cured two-component adhesive has 7.0 to 25.0% by weight of [CH2-O-] based on the total weight of the adhesive. n The proportion of units, where n is a number from 2 to 50.

[0053] According to a second embodiment, the present invention relates to a method according to a first embodiment, characterized in that the isocyanate reactive component of the two-component adhesive comprises or is composed of polyols, particularly polyester polyols, polyether polyols, hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, hydroxyl-containing reaction products of hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, and diisocyanates or mixtures of the above compounds.

[0054] According to a third embodiment, the present invention relates to a method according to a first or second embodiment, characterized in that the isocyanate component of the two-component adhesive comprises or is composed of therefrom. The monomeric polyisocyanate composition, particularly hexamethylene-1,6-diisocyanate, pentamethylene-1,5-diisocyanate, 1,4-butane diisocyanate, isophorone diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-2,2'-diisocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, or mixtures thereof; Composed of oligomeric polyisocyanates prepared from at least two monomeric polyisocyanates; The isocyanate-terminated prepolymer composition is prepared by reacting monomers and / or oligomeric polyisocyanates with isocyanate reactive compounds having >1 isocyanate reactive group per molecule, wherein the isocyanate reactive compound preferably comprises or is composed of polyols, more preferably hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, polyacrylates, polycarbonates, polyesters, polyurethanes and / or polyethers. Or a mixture of the above compounds The isocyanate-terminated prepolymer preferably has the [CH2-O-] structure defined in Example 1. n unit.

[0055] According to a fourth embodiment, the present invention relates to a method according to one of the foregoing embodiments, characterized in that [CH2-O-] n The number n in the unit is a number between 8 and 20.

[0056] According to a fifth embodiment, the present invention relates to a method according to one of the foregoing embodiments, characterized in that the two-component adhesive further comprises an organic solvent, a catalyst, a filler, a processing aid, an adhesion promoter, particularly a silane, a stabilizer, particularly an antioxidant, or a mixture thereof.

[0057] According to a sixth embodiment, the present invention relates to a method according to one of the foregoing embodiments, characterized in that one of the isocyanate reactive components or isocyanate components has an average molecular weight Mn of <1000 g / mol and an average functionality of >2, and in each case, the other component has an average molecular weight Mn of >1000 g / mol and a functionality of <4.

[0058] According to a seventh embodiment, the present invention relates to a method according to one of the foregoing embodiments, characterized in that the two-component adhesive has a stoichiometric ratio of isocyanate groups to isocyanate reactive groups between 0.8:1 and 2:1.

[0059] According to the eighth embodiment, the present invention relates to a method according to one of the foregoing embodiments, characterized in that the polyolefin of the single material layer is selected from the group consisting of or composed of polyethylene, polypropylene or mixtures thereof.

[0060] According to a ninth embodiment, the present invention relates to a method according to one of the foregoing embodiments, characterized in that the proportion of the polyolefin is 95.0 to 99.3% by weight and / or the proportion of the two-component adhesive is 0.70 to 10.0% by weight, preferably 1.0 to 5.0% by weight, based on the total weight of the single-material multilayer system in each case.

[0061] According to the tenth embodiment, the present invention relates to a single-material multilayer system that is obtained or obtainable by a method according to one of embodiments 1 to 9, particularly a recyclable single-material multilayer system.

[0062] According to the eleventh embodiment, the present invention relates to the use of the single-material multilayer system according to embodiment 10 as a preferred recyclable packaging material, particularly a food packaging material.

[0063] According to the twelfth embodiment, the present invention relates to the use of a two-component adhesive as described in any one of embodiments 1 to 7 in a single-material multilayer system, particularly for improving the recyclability of the single-material multilayer system, wherein the material of the single-material layer comprises polyolefin in a proportion of 80.0 to 99.3% by weight based on the total weight of the single-material multilayer system.

[0064] According to a thirteenth embodiment, the present invention relates to a method for obtaining recyclables from waste containing a single-material multilayer system, comprising the single-material multilayer system as described in embodiment 10, wherein the method includes the following steps: i. Grinding, washing, and optionally sterilizing waste containing a single-material multilayer system to obtain a mixture of materials; ii. Optionally classify the mixture of materials; iii. Optionally, the material mixture may be mixed with other components, particularly with polyolefins; iv. Further processing, particularly melting and extruding the material mixture, to obtain the recycled material.

[0065] According to the fourteenth embodiment, the present invention relates to a molded part obtained or obtainable by processing a recyclable material obtained or obtainable according to the method of embodiment 13.

[0066] Example

[0067] The present invention will be explained in more detail below with reference to the following embodiments.

[0068] Measurement methods Gel permeation chromatography (GPC): The weight-average and number-average molecular weights (Mw and Mn) of the obtained polymer are determined by gel permeation chromatography (GPC). The procedure is based on DIN 55672-1: "Gel permeation chromatography, Part 1 – Tetrahydrofuran as eluent". Polystyrene samples with known molecular weights are used for calibration. The polydispersity index (PDI) is calculated by the quotient of the weight-average molecular weight and the number-average molecular weight.

[0069] Unless otherwise stated, the number of hydroxyl groups (or OH groups) of the compound is determined according to DIN EN ISO 4629-2. In 5.1 and 5.5, N-methylpyrrolidone is substituted with pyridine, respectively, and in 5.2, the solvent for the catalyst is ethanol instead of methanol.

[0070] Material : The following raw materials and materials were used : Raw materials for the preparation of polyoxymethylene-polyalkylene copolymer The bimetallic cyanide (DMC) catalyst prepared according to Example 6 of WO2001 / 80994 A1 comprises zinc hexacyanocobaltate, tert-butanol, and polypropylene glycol with a Mn concentration of 1000 g / mol. Cyclopropylene carbonate (cPC), Chemical Abstracts Service number 108-32-7, Merck. Paraformaldehyde (pFA), Prefere Paraform GmbH & Co KG Propylene oxide (PO), Sigma-Aldrich

[0071] Raw materials for preparing single-layer materials BorShape ® FX1001: α-olefin terpolymer polyethylene (granules)

[0072] Single material layer Cast polypropylene (CPP) film: 50 μm thick unembossed cast polypropylene film PB81AB; Manufacturer: Profol GmbH, Material No. 15357005

[0073] Isocyanate reactive components Glycerin: Glycerin is a trifunctional low molecular weight polyol.

[0074] Baycoll ® AD 2047: Baycoll ® AD 2047 is a linear polyester polyol with two OH functional groups. The number of hydroxyl groups is approximately 55.0 mg KOH / g.

[0075] Acclaim ® Polyol 18200 N: Acclaim ®Polyol 18200 N is a linear polypropylene ether polyol with 2 OH functional groups. The number of hydroxyl groups is approximately 6.0 mg KOH / g.

[0076] Polyol 22: A linear polypropylene ether polyol with two OH functional groups. The number of hydroxyl groups is approximately 4.9 mg KOH / g.

[0077] Example 1 - Preparation of polyoxymethylene-polyalkylene copolymer with a total DMC catalyst loading of 1000 ppm and continuous addition of pFA and PO: In a 1.0 L pressure reactor, 10 g of pretreated pFA (pretreatment: 50 °C, 5 mbar, 1.5 h) and 300 mg of DMC catalyst were suspended in 150 g of cPC. The mixture was inertized with N2 (25 L / h) at 60 °C while stirring at 30 mbar for 30 min (500 rpm). The suspension was heated to 70 °C while stirring (1000 rpm). Once the reactor temperature was reached, 20 g of propylene oxide (8.8 wt%) was rapidly added to the suspension. The reaction was initiated by a temperature peak (“hot spot”) and a simultaneous pressure drop. The reactor temperature was then increased to 80 °C, and 208 g of PO was added at a metering rate of 0.9 g / min, along with 62 g of paraformaldehyde (as a 20% suspension in the cPC) at a metering rate of 1.7 g / min. After the additions were complete, the mixture was stirred continuously until the exothermic reaction subsided or the pressure remained at 80 °C. The product mixture was then removed and degassed on a rotary evaporator at 60°C and 10 mbar. The suspension cPC was removed under vacuum (thin-film evaporator, pre-evaporator: 150°C, main evaporator: 160°C, 2 mbar). This process was repeated several times, and the reaction products from five identical experiments were combined.

[0078] The average molecular weight is approximately Mn(GPC) = 2605 g / mol, and the PDI is 1.19.

[0079] Example 2 - Preparation of OH prepolymer based on raw materials from Example 1

[0080] 1200 g of the raw material from Example 1 was placed in a flat grinding container at 75°C. 0.23 g of 2-chloropropionic acid was added with stirring, followed by 107.5 g of Desmodur 44 M at 75°C. Stirring continued at 75°C until the NCO% value decreased to 0%. The viscosity of the prepolymer at 23°C was 46,060 mPas. The average molecular weight was approximately Mn(GPC) = 9600 g / mol. The OH value of the prepolymer was 14.0 mg KOH / g.

[0081] Isocyanate components Desmodur ® 44 M: Desmodur ® 44 M Liquid is a monomeric diisocyanate that is solid at room temperature and liquid above approximately 40°C. The NCO content is approximately 33.6% by weight.

[0082] Desmodur ® 2460 M: Desmodur ® 2460 M is a mixture of isomers of 2,4- and 4,4-diphenylmethane diisocyanate, which is liquid above 20°C. The NCO content is approximately 33.6% by weight.

[0083] Desmodur ® ultra N 3300: Desmodur ® Ultra N 3300 is an aliphatic polyisocyanate (HDI trimer) with a low residual monomer content of <0.1%. The NCO content is approximately 21.8% by weight.

[0084] Desmodur ® Ultra N 3600: Aliphatic low-viscosity polyisocyanate (HDI trimer) with low residual monomer content, <0.1%. NCO content is approximately 23.0% by weight.

[0085] Desmodur ® E 23: An aromatic polyisocyanate prepolymer based on diphenylmethane diisocyanate (MDI). The NCO content is approximately 15.4% by weight.

[0086] Example 3: Preparation of NCO prepolymer based on the raw materials of Example 1

[0087] At 75°C, 250 g of Desmodur 2460 M and 0.04 g of 2-chloropropionic acid were introduced into a flat container. Then, 750 g of the prepolymer from Example 2 was slowly added dropwise until the target NCO content of 7.3% was reached. The viscosity of the prepolymer at 23°C was 36,300 mPas. The average molecular weight was approximately Mn(GPC) = 7200 g / mol.

[0088] Preparation of two-component adhesives

[0089] Before preparing the adhesive, the raw materials used to prepare the two-component adhesive were heated at 60°C for 3 hours. The isocyanate reactive component and the isocyanate component were placed in a beaker and mixed. The mixture was stirred with a wooden spatula until a homogeneous mixture was obtained.

[0090] Examples of the present invention used for preparing two-component adhesives can be found in the table below.

[0091] Table 1: Preparation of two-component polyurethane adhesives

[0092] Examples 8 and 9 are comparative examples (V).

[0093] Preparation of Curing Two-Component Adhesives

[0094] The polyurethane adhesives of Examples 4 to 9 were cured in a Teflon shell (diameter: 15 cm / depth: 0.5 cm). The adhesive film was cured by storing it at 23°C and 50% relative humidity for 7 days, followed by storage at 60°C for 48 hours. After drying, the thickness of the corresponding adhesive film was approximately 100 µm.

[0095] Preparation of single-material multilayer systems

[0096] To prepare a single-material multilayer system, a manual laminator, K Control Coater Modell 623 / 624 (K101 / K202), was used. A first film (cast polypropylene film: 50µm thick cast polypropylene film; manufacturer: Profol GmbH) was clamped in the manual laminator. The film was DIN A4 size and corona-treated before adhesive application, resulting in a surface tension > 50 dyn. A beaded two-component adhesive was then applied to the upper edge of the first clamped film. The adhesive was then evenly distributed across the film using a doctor blade. The two-component adhesive was heated to 100°C using a heat gun (Steinel HL2002LE) to achieve a surface temperature of 60°C. In the next step, a second identical film was laminated onto the coated first film. The resulting composite was then stored at 60°C for 24 hours. After storage and cooling to room temperature, the composite strength was determined in a 180° peel test.

[0097] Determination of composite strength in 180° peel test

[0098] To determine the peel strength, the composite film was cut into strips 15 mm wide. The strips were then peeled at 100 mm / min at an angle of 2 × 90° (180°) using a Zwick Allround Table-top Peel Strength Tester (Model 5kN Allround Table-top BT2-FA005TH.A50.002) at 23°C, and the required force, in Newtons, was measured. The values ​​given are the average of five individual measurements. The determined composite strength can be found in the table below.

[0099] Table 2: Composite Strength

[0100] Sufficient composite strength is provided when a value of at least 0.5 N / 15 mm is achieved.

[0101] Method for obtaining recyclables from raw materials used in the preparation of single-material multilayer systems

[0102] Cut the cured two-component adhesive film into sheets measuring 0.5 cm × 0.5 cm using scissors. During extrusion, mix 0.75 g of the corresponding two-component adhesive from Examples 4 to 9 with 14.25 g of PE granules (BorShape). ® FX1001 hybrid extrusion. Extrusion was carried out in a laboratory extruder (Mikro Compounder / DSM Xplore / Model 2005) at a temperature of 200°C for 6 minutes. Extrusion produced uniform polymer strands.

[0103] Recycling quality assessment

[0104] A portion of the extruded polymer strand is pressed using a hydraulic press (manual lever press / Vogt Maschinenbau GmbH / LaboPress P150H) at 200°C for 2 minutes and 30 kN of pressure to form a polymer film with a thickness of 200 µm and a diameter of 5 cm. The polymer film obtained in this manner is then used to test uniformity after cooling. Similarly, recyclables can be produced directly from monolayer systems or waste containing monolayer systems. In this case, the adhesive and PE granules are replaced by the monolayer system (or waste containing monolayer systems).

[0105] The sample or polymer film was placed under a Nikon Ni-E optical microscope with a motorized stage, and optical photomicrographs of the sample surface were recorded under transmitted light. Four times magnification of the lens used was employed. To obtain statistically reliable data, an automatic plotting module was used for samples with a total area of ​​11.84 x 10.47 cm. 2The sample surface was studied using a module that stitched together 5 x 4 images. After image acquisition, automated image analysis was performed using Nikon NIS Elements BR version 5.4 software. Defects in the sample were identified by determining regions within the sample based on a threshold determined from the intensity of the rest of the sample. A threshold of 150 was applied for defects with optical density lower than the matrix optical density, and a threshold of 120 was used for defects with optical density higher than the film optical density. After separation, further size constraints were applied to the results, where features with an equivalent diameter less than 20 µm and a circularity less than 0.1 were excluded to remove artifacts. The filtered results were then calculated to give the number of defects, the defect area ratio, and the average equivalent diameter of the defects.

[0106] Table 3: Quality Assessment of Recyclables

[0107] Examples 10, 15 and 16 are comparative examples (V).

[0108] As can be seen from the results in Table 2, the recyclables according to the present invention exhibit significantly higher uniformity, which is manifested in a significantly smaller number of defects and total area compared to Comparative Examples 15 and 16.

Claims

1. A method for preparing a single-material multilayer system, particularly a recyclable single-material multilayer system, wherein, The method includes or comprises the following steps: I) Provide at least two single-material layers; II) Applying a two-component adhesive indirectly or directly to at least one of the two provided single-material layers, wherein the two-component adhesive comprises at least one isocyanate reactive component and at least one isocyanate component; III) The single-material layers are bonded together using the two-component adhesive, and the two-component adhesive is cured to obtain the single-material multilayer system; Its features are, The material of the single-material layer comprises a polyolefin, and the proportion of the polyolefin is 80.0% to 99.30% by weight based on the total weight of the single-material multilayer system. The proportion of the two-component adhesive is from 0.70% to 20.0% by weight based on the total weight of the single-material multilayer system. The isocyanate reactive component and / or isocyanate component contains [CH2-O-]. n unit, and The cured two-component adhesive has 7.0 to 25.0% by weight of [CH2-O-] based on the total weight of the adhesive. n Unit ratio, Where n is a number from 2 to 50.

2. The method according to claim 1, characterized in that, The isocyanate reactive component of the two-component adhesive comprises or consists of polyols, particularly polyester polyols, polyether polyols, hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, hydroxyl-containing reaction products of hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, and diisocyanates or mixtures of the above compounds.

3. The method according to claim 1 or 2, characterized in that, The isocyanate component of the two-component adhesive comprises or is composed of The monomeric polyisocyanate composition, particularly hexamethylene-1,6-diisocyanate, pentamethylene-1,5-diisocyanate, 1,4-butane diisocyanate, isophorone diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-2,2'-diisocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, or mixtures thereof; Composed of oligomeric polyisocyanates prepared from at least two monomeric polyisocyanates; The isocyanate-terminated prepolymer composition is prepared by reacting monomers and / or oligomeric polyisocyanates with isocyanate reactive compounds having >1 isocyanate reactive group per molecule, wherein the isocyanate reactive compound preferably comprises or is composed of polyols, more preferably hydroxyl-containing polyoxymethylene-polyoxyalkylene copolymers, polyacrylates, polycarbonates, polyesters, polyurethanes and / or polyethers. Or a mixture of the above compounds The isocyanate-terminated prepolymer preferably has the [CH2-O-] structure as defined in claim 1. n unit.

4. The method according to any one of the preceding claims, characterized in that, The [CH2-O-] n The number n in the unit is a number between 8 and 20.

5. The method according to any one of the preceding claims, characterized in that, The two-component adhesive also includes organic solvents, catalysts, fillers, processing aids, adhesion promoters, especially silanes, stabilizers, especially antioxidants, or mixtures thereof.

6. The method according to any one of the preceding claims, characterized in that, The isocyanate reactive component or one of the isocyanate components has an average molecular weight Mn of <1000 g / mol and an average functionality of >2, and in each case, the other component has an average molecular weight Mn of >1000 g / mol and a functionality of <4.

7. The method according to any one of the preceding claims, characterized in that, The two-component adhesive has a stoichiometric ratio of isocyanate groups to isocyanate reactive groups between 0.8:1 and 2:

1.

8. The method according to any one of the preceding claims, characterized in that, The polyolefin in the single material layer is selected from the group consisting of or composed of polyethylene, polypropylene, or mixtures thereof.

9. The method according to any one of the preceding claims, characterized in that, The proportion of the polyolefin is 95.0 to 99.3% by weight and / or the proportion of the two-component adhesive is 0.70 to 10.0% by weight, preferably 1.0 to 5.0% by weight, based on the total weight of the single-material multilayer system in each case.

10. A single-material multilayer system, particularly a recyclable single-material multilayer system, obtained or obtainable by the method according to any one of claims 1 to 9.

11. Use of a single-material multilayer system according to claim 10 as a preferred recyclable packaging material, particularly a food packaging material.

12. Use of a two-component adhesive as described in any one of claims 1 to 7 in a single-material multilayer system, particularly for improving the recyclability of a single-material multilayer system, wherein, The material of the single-material layer comprises polyolefin in a proportion of 80.0 to 99.3% by weight of the total weight of the single-material multilayer system.

13. A method for obtaining recyclables from waste containing a single-material multilayer system, comprising the single-material multilayer system according to claim 10, wherein, The acquisition includes the following steps: i. Grinding, washing, and optionally sterilizing waste containing a single-material multilayer system to obtain a mixture of materials; ii. Optionally classify the mixture of materials; iii. Optionally, the material mixture may be mixed with other components, particularly with polyolefins; iv. Further processing, particularly melting and extruding the material mixture, to obtain the recycled material.

14. A molded part, obtained or obtainable by processing a recyclable material obtained or obtainable by the method of claim 13.

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