Method for producing cross-linked adhesive

Abstract

The invention relates to a method for preparing a cross-linked adhesive, in particular in the scope of a 3D printing process, comprising the method steps: a) preparing a prepolymer composition comprising one or more polyurethane prepolymers wherein the one or more polyurethane prepolymers can be prepared by the reaction of a starting composition, the starting composition includes i) one or more diisocyanate compounds, ii) one or more first diol compounds, where the first diol compounds are selected from the group consisting of diols having at least one C-C double bond / molecule, and iii) one or more second diol compounds different from the first diol compounds, where the second diol compounds are selected from the group consisting of diols having at least one C-C double bond / molecule. And b) cross-linking the polyurethane prepolymer in the prepolymer composition by reaction of the C-C double bond of the first diol compound with one or more multifunctional thiol compounds to obtain a cross-linked polyurethane polymer.

Description

[0001] The present invention relates to a method for preparing a crosslinked adhesive (especially within the scope of a 3D printing process), a method for preparing a tape based on this method and / or a method for preparing a crosslinked three-dimensional adhesive structure in a 3D printing process, and also includes the crosslinked adhesive prepared by this method. In addition, the corresponding tape and / or the corresponding crosslinked three-dimensional adhesive structure are disclosed, as well as the use of a prepolymer composition as a printing material in a 3D printing process for manufacturing a three-dimensional adhesive structure.

[0002] The joining of individual elements is a core method in manufacturing technology. In addition to other methods such as welding and soldering, adhesive bonding technology, i.e., the joining method using adhesives, is of great significance at present. As an alternative to, for example, an amorphous adhesive applied from a tube, so-called tapes are provided here, and the adhesive action of the tape is based on the adhesive used.

[0003] In a large number of technical applications, polyurethane systems have proven to be excellent base materials for manufacturing high-performance adhesives, as disclosed in the document EP3155034A1. These polymer compounds are usually obtained by polyaddition of polyols and polyisocyanates and generally have physicochemical properties that can be used in adhesive compounds for various high-performance applications, especially in the field of electronic products. In addition to generally very favorable adhesive properties, these properties also include light resistance, resistance to harsh climatic conditions, and resistance to various chemicals, etc. Therefore, the physicochemical properties of polyurethanes can be specifically adapted to the corresponding application requirements by selecting raw materials in many cases, which is considered to be particularly advantageous.

[0004] When preparing a polyurethane-based adhesive, a so-called polyurethane prepolymer is usually first prepared, that is, a polyurethane with a relatively low average molecular weight set by the mixing ratio of raw materials and reaction conditions. Thus, the polyurethane prepolymer, which is usually hydroxyl-terminated and still substantially meltable, can still be processed well, for example, by mixing the polyurethane prepolymer with other components such as an adhesive resin. Among them, the resulting still-meltable composition can be efficiently formed, for example, to form a subsequent adhesive layer of a tape. The adhesive is obtained by crosslinking the polyurethane prepolymer or prepolymer composition. In the prior art, it is usually achieved by crosslinking a hydroxyl-terminated polyurethane prepolymer using a polyfunctional isocyanate.

[0005] Although the polyurethane-based adhesives known in the prior art have various advantages, this system is still considered disadvantageous in some aspects.

[0006] In many cases, limited by the reactivity of the polyfunctional isocyanates used, the crosslinking of polyurethane prepolymers known in the prior art exhibits a strong correlation with the ambient air humidity, which may be disadvantageous for the reproducibility of crosslinking. In addition, other processing steps are usually required for crosslinking, in which polyfunctional isocyanates are added, and solvents are usually used in this process. However, the addition of polyfunctional isocyanates initiates the crosslinking reaction, thereby starting to reduce the processability and the so-called pot life. It is also often found that the crosslinking in the classical manner may take a relatively long time to reach the desired final degree of crosslinking, which largely determines the final mechanical properties of the crosslinked adhesive, and in the methods known in the prior art, this often lasts for more than two weeks.

[0007] In addition, in many cases, adhesives based on polyurethanes prepared by crosslinking processes known in the prior art are disadvantageously limited in terms of other additives that can be added to the polyurethane prepolymer composition before crosslinking, because hydroxyl groups, such as those in resins or plasticizers, in particular have a negative impact on crosslinking.

[0008] The above aspects especially mean that adhesives based on polyurethanes known in the prior art generally cannot be used in additive manufacturing processes, commonly referred to as 3D printing processes. This is generally regarded as a disadvantage because these modern manufacturing processes - like many other industries - also open up many interesting applications in the field of adhesive technology, especially in the targeted formation of three-dimensional bonding structures, the shape and size of which can be precisely matched to the intended application, which is considered particularly advantageous in the field of electronics production.

[0009] It is generally not feasible to process crosslinked adhesives based on polyurethanes suitable for the required application purposes in 3D printing processes. This means that only meltable polyurethane prepolymers or corresponding polyurethane prepolymer compositions can be shaped using a 3D printer. However, due to operational and technical reasons, the addition of the polyfunctional isocyanates required for crosslinking cannot be carried out after shaping. At the same time, the addition time of the polyfunctional isocyanates cannot be too early to avoid crosslinking and affecting the processing performance in the case of a short pot life. Since there is a risk of blockage in the fluid supply line, it is also not realistic to supply the already crosslinked adhesive through the fluid supply line. Therefore, the equipment requirements for 3D printing equipment will increase significantly because it must mix the polyurethane prepolymer composition and the polyfunctional isocyanates as evenly as possible immediately before shaping, and in many cases, the required solvents will also make the use of 3D printers more difficult. This will also greatly increase the cleaning and maintenance workload because there is still a possibility of being contaminated by over-crosslinked adhesives even in the case of late mixing.

[0010] Furthermore, considering production costs, most additive manufacturing processes available for printing polyurethane prepolymer compositions are not carried out in an inert gas environment, especially in large-scale production, and the 3D printing equipment used usually does not have such conditions. However, due to the susceptibility of the crosslinking chemistry known in the prior art, this also has a particularly adverse effect on the reproducibility of the printing quality, especially for many high-performance applications, which would be unacceptable. In addition, the curing time required to achieve the desired final degree of crosslinking is relatively long, which, according to the inventors' assessment, would impede reasonable use in additive manufacturing.

[0011] The main task of the present invention is to eliminate or at least reduce the above-mentioned disadvantages of the prior art.

[0012] In particular, the technical problem to be solved by the present invention is to provide a method for producing a crosslinked adhesive based on polyurethane, which produces a crosslinked adhesive having the advantages of an adhesive based on polyurethane without showing the disadvantages of the crosslinking processes known in the prior art during production.

[0013] Another technical problem to be solved by the present invention is that the disclosed method should also exhibit good reproducibility under changing environmental conditions and a higher tolerance to the use of different additives.

[0014] In addition, another technical problem to be solved by the present invention is that the disclosed method should be able to produce a crosslinked adhesive having excellent adhesive properties.

[0015] In addition, the technical problem to be solved by the present invention is that the disclosed method should be able to produce a crosslinked adhesive in a particularly time-saving and cost-effective manner, especially should be able to improve the curing time until the final degree of crosslinking is obtained. What is desired here is that such a method should still provide particularly high process reliability.

[0016] Another technical problem to be solved by the present invention is that in the provided method, the production of the crosslinked adhesive should be advantageous from the perspective of environmental and occupational safety, especially should reduce the risk of contact or release of isocyanate compounds and the need for solvents.

[0017] In addition, another technical problem to be solved by the present invention is that the provided method should be able to prepare a crosslinked adhesive having favorable biodegradability.

[0018] In addition, another technical problem to be solved by the present invention is that the provided method should be able to prepare a crosslinked adhesive having improved damping properties.

[0019] In particular, the technical problem to be solved by the present invention is that the provided method should also be able to effectively prepare a crosslinked adhesive within the scope of the 3D printing process, so that 3D printing of an adhesive structure can be achieved with a polyurethane-based adhesive. In this case, it is desirable that the provided method places as few equipment requirements as possible on the 3D printing equipment used.

[0020] The technical problem to be solved by the present invention is to provide a crosslinked adhesive that can be prepared by the proposed method, which has a polyurethane-based adhesive, but can be produced in a particularly time-saving and cost-effective manner and has a high degree of reproducibility.

[0021] The supplementary technical problem to be solved by the present invention is to provide two methods for preparing a tape or a three-dimensional adhesive structure based on the provided method. Here, the second technical problem to be solved by the present invention is to further provide the corresponding tape and three-dimensional adhesive structure generated by the method.

[0022] In addition, the second technical problem to be solved by the present invention is to provide the use of a polyurethane prepolymer composition as a printing material in a 3D printing process for generating a three-dimensional adhesive structure.

[0023] The inventors of the present invention have now found that, surprisingly, the aforementioned technical problems can be solved by using such a polyurethane prepolymer in a prepolymer composition when preparing an adhesive. The polyurethane prepolymer is not only composed of a diisocyanate compound and a conventionally used diol compound, but also contains C-C double bonds in its polymer chain, which are purposefully introduced by polymerizing an unsaturated diol with at least one C-C double bond, and the polyurethane prepolymer is then crosslinked by a thiol click chemical reaction, that is, by reacting with one or more polyfunctional thiol compounds, as defined in the claims.

[0024] The inventors have found that crosslinked adhesives can surprisingly be obtained by using the method according to the invention. The crosslinked adhesives have the advantages of polyurethane-based adhesives, particularly excelling in adhesive technical properties, without showing the drawbacks of the crosslinking chemistries known in the prior art during preparation. In particular, the sensitivity to air humidity is reduced, and the use of additives with hydroxyl groups is also made easier. Crosslinking by reacting the C-C double bonds of the polyurethane prepolymer with one or more polyfunctional thiol compounds can be triggered, for example, by radiation. This crosslinking can in particular also solve the problem of too short a pot life under radiation activation conditions and enable time-saving and cost-effective crosslinking within a very short curing time. Furthermore, it is possible to advantageously dispense with isocyanates during crosslinking and, if necessary, carry out the crosslinking step solvent-free. Compared with another method of converting polyurethane prepolymers into crosslinked polyurethanes by free radical polymerization of terminal double bonds without using polyfunctional thiol compounds, the present invention can not only obtain a wider range of possible activation mechanisms but also further reduce the sensitivity of the crosslinking reaction to oxygen, especially when using the thiol-Michael addition method.

[0025] In particular, the method according to the invention can be used to efficiently prepare three-dimensional adhesive structures from crosslinked polyurethane-based adhesives by three-dimensional printing technology, wherein the equipment requirements of the three-dimensional printing device are relatively low because, for example, only a radiation source needs to be provided for radiation-activated crosslinking, and the crosslinking can also be carried out downstream. In particular, the method according to the invention can also be used to obtain crosslinked adhesives with good biodegradability.

[0026] Furthermore, the inventors have also found that in a specific method implementation, a crosslinked adhesive is surprisingly formed, which surprisingly has improved damping properties compared to conventionally prepared polyurethane-based crosslinked adhesives. Without wishing to be bound by this theory, the inventors believe that this is because in the method according to the invention, crosslinking does not occur through terminal hydroxyl groups. According to the hypothesis, since the unsaturated diols having at least one C-C double bond are substantially randomly present in the chains of the polyurethane prepolymer, crosslinking mainly occurs along the polymer chains, thereby obtaining a network with a large number of freely movable side chains, which the inventors believe has better damping properties. Among them, according to the inventors' understanding, if raw materials with side chains, such as diols based on polyfarnesene or fatty acid esters, are also used in the polyurethane prepolymer, this effect can be further enhanced.

[0027] Thus, the above technical problem is solved by the subject matter defined in the claims of the present invention. Preferred design embodiments according to the invention are given in the dependent claims and the following description.

[0028] This so-called preferred embodiment is combined in a particularly preferred embodiment with features of other so-called particularly preferred embodiments. Thus, a combination of two or more of the following so-called particularly preferred embodiments is further particularly preferred. Some embodiments are equally preferred, in which features that are called preferred to any extent in one embodiment are combined with one or more further features that are called preferred to any extent in other embodiments. The features of the preferred adhesives, tapes, three-dimensional adhesive structures, and applications are given by the features of the preferred method.

[0029] The specific amounts or proportions of certain elements, such as diisocyanate compounds or first diol compounds, and preferred embodiments of such elements are disclosed below, and thus the specific amounts or proportions of the preferred design elements are also particularly disclosed. It is also disclosed that, in the corresponding total amounts or total proportions of the elements, at least some of the elements can be of a preferred design, and in particular it is disclosed that the elements of a preferred design in the specific total amounts or total proportions can be present in specific amounts or proportions.

[0030] The present invention relates to a method for preparing a crosslinked adhesive, particularly within the scope of a 3D printing process, the method comprising the method steps:

[0031] a) preparing a prepolymer composition comprising one or more polyurethane prepolymers, wherein the one or more polyurethane prepolymers can be prepared by the reaction of a starting composition comprising:

[0032] i) one or more diisocyanate compounds,

[0033] ii) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols having at least one C-C double bond / molecule, and

[0034] iii) one or more second diol compounds different from the first diol compounds, and

[0035] b) crosslinking the polyurethane prepolymers in the prepolymer composition by the reaction of the C-C double bonds of the first diol compounds with one or more polyfunctional thiol compounds to obtain a crosslinked polyurethane polymer.

[0036] In the method according to the invention, a prepolymer composition is first prepared or provided, which is subsequently crosslinked to obtain a crosslinked adhesive. The prepolymer composition comprises other components in addition to the polyurethane prepolymers, and these other components should be included in the crosslinked adhesive during the subsequent crosslinking process, such as adhesive resins, pigments, or other additives that a person skilled in the art should add according to the desired application purpose. The important components of the prepolymer composition for the present invention are the special polyurethane prepolymers.

[0037] Based on professional common sense, those skilled in the art are very familiar with polyurethane itself, the polyurethane group from which the name polyurethane is derived, and its basic chemical composition. In particular, they are also very familiar with the concept of polyurethane prepolymers. The polyurethane prepolymer used in the present invention is a copolymer prepared or preparable from a specific starting composition through a polymerization reaction, more precisely through an addition reaction. Herein, this expression should also include compounds that are also referred to as polyurethane pre-oligomers due to their chain length, because the distinction between oligomers and polymers is not fixed in any case and ultimately varies according to the will, so there is no need to make a distinction here. According to professional understanding and the usual procedures in the technical field, it is more appropriate to define such copolymers by the preparation process or the raw materials used for preparation, because it is basically impossible to comprehensively define the corresponding materials in any other conclusive way.

[0038] According to this common practice in the art, the preparability here refers to the starting composition. According to the understanding of those skilled in the art, the starting composition includes all independent compounds that are converted into the constituent units of the polyurethane prepolymer during the polymerization process. Sometimes, the corresponding starting composition for preparing the copolymer is also referred to as a monomer composition, but this term is not used in the present invention because, in particular, many commonly used diols, such as the compound used as the second diol compound, are, strictly speaking, already oligomers or polymeric compounds in themselves. According to the understanding of those skilled in the art, the starting composition does not include any other components that may be present in the reaction mixture during the polymerization process but are not added to the polyurethane prepolymer during the polymerization process, such as solvents or other non-reactive compounds.

[0039] According to the understanding of those skilled in the art, these components in the starting composition defined above are all "one or more". The term "one or more" refers to the chemical nature of the corresponding compound, rather than its amount of substance, which is common practice in the industry. For example, the starting composition may only contain hexamethylene diisocyanate as the diisocyanate compound, which means that the starting composition contains a large number of corresponding molecules.

[0040] As understood by those skilled in the art, the prepolymer composition, or more precisely the polyurethane prepolymer, remains uncrosslinked in the prepolymer composition but can form a crosslinked adhesive through crosslinking. Those skilled in the art understand that the term "non-crosslinked" refers to chemical crosslinking, i.e., individual copolymer chains are covalently linked to each other to form a network, rather than any physical crosslinking of the copolymer chains, such as through entanglement, phase separation, or crystallization, so that the polyurethane prepolymer has regular fusibility. Those skilled in the art understand that the uncrosslinked polyurethane prepolymer is not necessarily linear and can also be a branched copolymer chain, especially if the starting composition contains high-value polyisocyanates and / or polyols in addition to diisocyanates and diols. Even though the transition from the branched copolymer chain to the crosslinked network in the crosslinked adhesive may seem ambiguous in theory, for those skilled in the art, the non-crosslinked state or crosslinked state is relatively easy to determine in practice, and those skilled in the art can determine it by methods such as temperature-related rheological properties or simple solubility tests. In the crosslinked adhesive, the molecular weight of the resulting crosslinked polyurethane increases significantly, so it is usually no longer soluble in organic solvents or can no longer be melted, and thus only liquefaction that is substantially irreversible can be achieved through decomposition.

[0041] The inventors hereby propose a range for the average molar mass of the polyurethane prepolymer, and by this method, the inventors can achieve a particularly advantageous method implementation empirically. Therefore, a preferred method according to the present invention is one in which the one or more polyurethane prepolymers have an average molar mass M 4 ranging from 1.0×10 4 to 8.0×10 4 g / mol as determined by GPC, preferably ranging from 1.5×10 4 to 6.0×10 4 g / mol, and particularly preferably ranging from 2.0×10 4 to 4.0×10 W g / mol.

[0042] Within the scope of the present invention, all the specifications for the weight-average molar mass M W are based on the determination by gel permeation chromatography (GPC). The determination is carried out with degassed tetrahydrofuran (THF) as the mobile medium, an injection volume of 50 µL, a sample concentration of 3 g / L, a flow rate of 1 mL / min, a temperature of 25 °C, and the system consists of a PSS-SECcurity 1260 HPLC pump, a PSS SDV 10 µm ID 8 mm×50 mm precolumn, a PSS SDV 5 µm 10 3 Å ID 8 mm×300 mm, a PSS SDV 5 µm 10 5 Å ID 8 mm×300 mm, a PSS SDV5 µm 106 An ID of 8 mm×300 mm and a SECcurity differential refractive index detector (RI). Data was recorded and analyzed using PSS-WinGPC UniChrome version 8.4 software. Calibration was performed using polystyrene standards and converted to polystyrene calibration uniformly using the Mark Houwink coefficients K and α.

[0043] In the process according to the invention, a crosslinked binder is prepared from a prepolymer composition by crosslinking a polyurethane prepolymer. The crosslinked binder includes, in addition to any other components of the prepolymer composition and its reaction products, a crosslinked polyurethane polymer. Those skilled in the art will understand that the crosslinked binder can also be a polyurethane copolymer, depending on the form of crosslinking or other components of the crosslinked binder. In the simplest case, the obtained crosslinked polyurethane polymer constitutes the crosslinked binder. However, the preferred method according to the invention is as follows, wherein the mass fraction (or combined mass fraction) of the crosslinked polyurethane polymer contained in the crosslinked binder with respect to the total mass of the crosslinked binder is in the range of 30% to 100%, preferably in the range of 40% to 100%, and particularly preferably in the range of 50% to 100%.

[0044] Different from the prior art, the crosslinking in the method of the present invention is not or at least not completely, preferably not at all, carried out by reacting with a polyfunctional isocyanate, but is based on the so-called Thiol-Click chemistry.

[0045] The scheme of the so-called Thiol-Click chemistry is known to those skilled in the art and is based on the thiol-ene reaction, in which a thiol reacts with an alkene to form a thioether. The thiol-ene reaction generally allows a high yield under good selectivity and rapid reaction rate. The thiol-ene reaction can be carried out by radical addition or a catalytic Michael reaction, and the catalytic Michael reaction is based on an anionic mechanism.

[0046] However, typical polyurethane prepolymers cannot actually be crosslinked by free radical polymerization or anionic thiol-ene reaction. This can only be achieved by adding a C-C double bond to a specific polyurethane prepolymer using a first diol compound.

[0047] The inventors have recognized that, considering the crosslinking step and the adjustable physicochemical properties in the crosslinked binder, not only the first diol compound but also at least a second diol compound should be used. By means of the second diol compound, the concentration of the units derived from the first diol compound in the polyurethane prepolymer can be controlled, thereby controlling the concentration of C-C double bonds. Those skilled in the art understand that the expression "different from the first diol compound" means that the second diol compound does not fall within the definition scope of the first diol compound. Two different diol compounds, for example, each being a diol with terminal C-C double bonds in each molecule, are not the first and second diol compounds in the sense of the present invention, but two different first diol compounds.

[0048] The polyurethane obtained in method step b) is crosslinked, and the crosslinked binder containing these polyurethanes produced according to the process of the present invention is also crosslinked. The understanding of those skilled in the art is that this means that the polyurethane prepolymer has been at least partially crosslinked, which is the result of method step b), and method step b) is inevitably stipulated according to the present invention. According to the understanding of those skilled in the art, this does not require achieving the theoretically maximum possible crosslinking, i.e., the complete crosslinking of the binder. Therefore, any crosslinking carried out during method step b) according to the requirements defined above is sufficient, and thus the system in which the crosslinking reaction occurs is also regarded as crosslinked in the sense of the present invention.

[0049] The components used in the starting composition will be described in detail below. In this regard, the inventors have successfully determined, in each case, particularly preferred embodiments and the mass fractions of the respective components. During the process of the method according to the present invention, favorable polyurethane prepolymers or high-performance crosslinked binders can be obtained with these components. According to industry practice, the mass fraction is specified, in each case, as the total mass fraction of one or more components, thereby indicating that the mass fractions of the correspondingly formed components together meet the corresponding criteria. In the absence of other information, the mass of the starting composition is used as the reference system in each case.

[0050] To obtain a crosslinked binder with favorable biodegradability, the inventors have pre-judged that it is appropriate to use aliphatic compounds instead of isocyanates. Therefore, according to a preferred method of the present invention, the diisocyanate compound is selected from the group of aliphatic diisocyanates.

[0051] Especially in cases where biodegradability is not emphasized, in addition to aliphatic diisocyanates, aromatic diisocyanates can also be used, which allows for more flexible adjustment of physical and chemical properties. However, according to the inventors' assessment, in these cases, it is also preferably not to choose an overly high proportion. Therefore, a preferred method according to the present invention is one in which the starting composition contains one or more aromatic polyisocyanate compounds having a total mass fraction of 30% or less, particularly preferably 20% or less, and very particularly preferably 15% or less, based on the mass of the starting composition, and / or in which the total mass fraction of the aromatic polyisocyanate compounds in the starting composition relative to the mass of the starting composition is 10% or less, particularly preferably 5% or less, and very particularly preferably 1% or less.

[0052] Taking into account that the average molar mass of the polyurethane prepolymer will be affected, the process according to the present invention is preferred, in which the starting composition contains one or more diisocyanate compounds, preferably aliphatic diisocyanates, having a total mass fraction between 1% and 30%, preferably between 4% and 20%, and particularly preferably between 5% and 15%, based on the mass of the starting composition.

[0053] In addition, higher-value polyisocyanates can also be used in the starting composition to adjust physical and chemical properties. However, according to the inventors' assessment, the branching of the resulting polyurethane prepolymer should be minimized. For this purpose, a preferred method according to the present invention is one in which the starting composition contains one or more polyisocyanate compounds having three or more isocyanate groups, having a total mass fraction of 10% or less, particularly preferably 5% or less, very particularly preferably 3% or less, and especially preferably 0.5% or less, based on the mass of the starting composition, and / or in which the total mass fraction of the polyisocyanate compounds having three or more isocyanate groups in the starting composition relative to the mass of the starting composition is 10% or less, particularly preferably 5% or less, and very particularly preferably 1% or less.

[0054] In principle, a large number of suitable diisocyanate compounds are known to those skilled in the art. However, according to the inventor's assessment, preferably, in the method according to the present invention, one or more diisocyanate compounds are selected from hexamethylene diisocyanate, 1,6 - diisocyanato - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S) - ethyl 2,6 - diisocyanatohexanoate, (R) - ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane), 4,4′-methylenebis(phenyl isocyanate), toluene - 2,4 - diisocyanate, naphthalene - 1,5 - diisocyanate and meta - tetramethylxylene diisocyanate, preferably selected from the following group: hexamethylene diisocyanate, 1,6 - diisocyanato - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S) - ethyl 2,6 - diisocyanatohexanoate, (R) - ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane) and 4,4′-methylenebis(phenyl isocyanate). In order to obtain a cross - linked adhesive with good biodegradability, according to the inventor's assessment, the method according to the present invention is particularly preferred, in which one or more diisocyanate compounds are selected from the group consisting of hexamethylene diisocyanate, 1,6 - diisocyanato - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S) - ethyl 2,6 - diisocyanatohexanoate and (R) - ethyl 2,6 - diisocyanatohexanoate. Additionally or alternatively, preferably, in the method according to the present invention, the diisocyanate compound is selected from diisocyanates having two or more, preferably three or more alkyl groups, preferably methyl groups, along the main chain.

[0055] According to the inventor's assessment, it is preferred to use shorter diisocyanate compounds, and thus preferably, in the method according to the present invention, one or more diisocyanate compounds are selected from the group consisting of aliphatic diisocyanates having 3 to 20 carbon atoms, preferably 4 to 18 carbon atoms, especially 5 to 15 carbon atoms.

[0056] In order to obtain a cross - linked adhesive with advantages in terms of sustainable development, the inventor suggests using bio - based diisocyanate compounds, which are very suitable for the method of the present invention. Therefore, preferably, in the method according to the present invention, one or more diisocyanate compounds are produced from renewable raw materials, and the preparation process preferably includes the conversion of plant biomass.

[0057] According to the assessment of the inventors, another particular advantage of the present invention is that subsequent crosslinking does not require terminal hydroxyl groups. Thus, in addition to diols and diisocyanates, monofunctional alcohols or isocyanates can also be used in the starting composition. These monofunctional building blocks can terminate the polymer chains obtained by the polymerization reaction, thereby effectively adjusting the required average molar mass. In addition, by using these monofunctional compounds, polyurethane prepolymers can be obtained whose ends carry neither hydroxyl groups nor isocyanate groups, which is particularly advantageous for the storage stability of the polyurethane prepolymers. Therefore, a preferred method according to the present invention is one in which the starting composition comprises one or more monofunctional compounds selected from the group consisting of monofunctional alcohols and monofunctional isocyanates, which preferably have a total mass fraction of 0.1% or more, preferably 1% or more, particularly preferably 3% or more, relative to the mass of the starting composition, and / or a total amount of substance in the range from 0.5*[A] to 1.5*[A], preferably from 0.8*[A] to 1.2*[A], particularly preferably from 0.95*[A] to 1.05*[A], where [A] is the total amount of substance of the terminal OH groups or isocyanate groups of the polyurethane prepolymer, and [A] can be determined by measurement or estimated using typical simulation methods to set the characteristics of, for example, the reference sample.

[0058] According to the assessment of the inventors, in order to obtain a particularly advantageous polyurethane prepolymer or a favorable crosslinking adhesive, the first diol compound is preferably designed to be rather short. In this way, the first diol compound can not only introduce the double bonds required for crosslinking into the polyurethane prepolymer, but also maintain a relatively high density of polyurethane groups in the polyurethane (pre)polymer. Due to the relatively rigid functional groups and the formation of hydrogen bonds in the high-density structure, so-called hard segments are produced, which is favorable for improving the adhesive properties of the crosslinking adhesive. In this context, a preferred method according to the present invention is first of all one in which the first diol compound is selected from diols having 4 to 60 carbon atoms, preferably 5 to 30 carbon atoms, particularly preferably 6 to 10 carbon atoms. In addition, in the method according to the present invention, the first diol compound is selected from diols having a molar mass in the range from 70 to 750 g / mol, preferably from 100 to 500 g / mol, particularly preferably from 140 to 250 g / mol.

[0059] Particularly preferred is a method according to the present invention in which one or more first diol compounds are selected from the group consisting of diols having one C-C double bond per molecule. As an alternative or in addition, preferred is a method according to the present invention in which one or more first diol compounds are selected from the group consisting of diols having one, preferably exactly one, terminal C-C double bond per molecule. As an alternative or in addition, particularly preferred is a method according to the present invention in which one or more first diol compounds are selected from the group consisting of aliphatic diols.

[0060] According to the inventor's evaluation, (meth)acrylates, allyl ethers, and diols containing at least one alkenyl group are particularly suitable as the first diol compound, and monomeric compounds are preferred in each case. Therefore, a preferred method according to the present invention is one in which one or more first diol compounds are selected from the group consisting of acrylates, methacrylates, allyl ethers, vinyl ethers, and diols containing at least one alkenyl group, preferably from the group consisting of methacrylates and allyl ethers.

[0061] Essentially independent of the specific choice of the first diol compound, a preferred method according to the present invention is one in which the starting composition comprises one or more first diol compounds having a total mass fraction in the range of 0.05% to 20%, preferably in the range of 0.5% to 6%, and more preferably in the range of 1% to 3.5% based on the mass of the starting composition.

[0062] However, considering the crosslinking kinetics, the resulting adhesion properties, and the possibility of adjusting favorable biodegradability, the inventor believes that it is preferably not to use monomeric diols having multiple groups that can be transformed during the thiol click reaction. Particularly advantageously, the content of monomeric second diols having two or more C-C double bonds, especially two or more terminal C-C double bonds, in each molecule is kept at a relatively low level. Accordingly, a preferred method according to the present invention is one in which the starting composition comprises one or more diols, preferably monomeric diols, having two or more C-C double bonds in each molecule, and the diols have a total mass fraction of 30% or less, particularly preferably 20% or less, and very particularly preferably 10% or less based on the mass of the starting composition, and / or in which the total mass fraction of the diols having two or more C-C double bonds in each molecule in the starting composition is 10% or less, particularly preferably 5% or less, and very particularly preferably 1% or less based on the mass of the starting composition.

[0063] It can be seen that the advantage of the present invention lies in being very flexible with respect to other diols, i.e., the second diol compound, and thereby enabling flexible adjustment of the physicochemical properties according to the corresponding required requirements. Those skilled in the art should understand that the second diol compound is preferably distinguished from the first diol compound such that it completely does not include C-C double bonds, thereby referring to saturated diols. Therefore, a preferred method according to the present invention is one in which the second diol compound is selected from the group consisting of saturated diols.

[0064] In principle, the second diol compound can be either a relatively short molecule, a so-called chain extender, or an oligomeric or polymeric diol, and these can also be mixed with each other. According to the inventor's evaluation, the use of oligomers and polymeric diols is particularly advantageous here. For a specific application, a preferred method according to the present invention is one in which the one or more second diol compounds are selected from the group consisting of saturated diols having 5 to 600 carbon atoms, preferably 8 to 350 carbon atoms, and particularly preferably 10 to 250 carbon atoms. However, a particularly preferred method according to the present invention is one in which one or more second diol compounds are selected from the group consisting of diols having a weight-average molar mass M W in the range of 200 to 6000 g / mol, preferably 300 to 4500 g / mol, and particularly preferably 400 to 3000 g / mol as determined by GPC.

[0065] Most particularly preferably, such compounds present in amorphous or semi-crystalline form are used for the oligomeric or polymeric second diol compounds. A preferred method according to the present invention is one in which the second diol compounds are selected from the group consisting of amorphous or semi-crystalline, preferably amorphous diols.

[0066] Basically independent of the specific choice of the second diol compound, a preferred method according to the present invention is one in which the starting composition comprises one or more second diol compounds having a total mass fraction in the range of 50% to 99%, preferably in the range of 60% to 97%, and more preferably in the range of 70% to 95% based on the mass of the starting composition. However, it is particularly preferred to use saturated diols and in this regard a preferred method according to the present invention is one in which the total mass fraction of the saturated diol is in the range of 50 to 99%, preferably in the range of 60 to 97%, and particularly preferably in the range of 70 to 95% based on the mass of the starting composition.

[0067] Similar to the above description of polyisocyanates, higher-valued polyols can also be used in the starting composition to adjust the physicochemical properties. However, according to the inventor's evaluation, the branching of the resulting polyurethane prepolymer should be minimized in this case. For this purpose, a preferred method according to the present invention is one in which the starting composition comprises one or more polyol compounds having three or more hydroxyl groups, which have a total mass fraction of 30% or less, particularly preferably 15% or less, very particularly preferably 3% or less, and especially preferably 0.5% or less based on the mass of the starting composition, and / or in which the total mass fraction of the polyol compounds having three or more hydroxyl groups in the starting composition is 10% or less, particularly preferably 5% or less, and very particularly preferably 1% or less based on the mass of the starting composition.

[0068] According to the inventor's assessment, polyester diols or polyether diols are particularly suitable for the second diol compound and sometimes also for the first diol compound, because these diols can produce crosslinked adhesives with good adhesion properties. Therefore, a preferred method according to the present invention is one in which the first diol compound and / or the second diol compound, preferably the second diol compound, is selected from the group consisting of diols having one or more, preferably two or more, particularly preferably a plurality of functional groups selected from ether groups and ester groups, preferably ester groups, and / or in which the first diol compound and / or the second diol compound, preferably the second diol compound, is selected from polyester diols and polyether diols, preferably polyester diols.

[0069] According to the inventor's assessment, it is particularly advantageous to also use hydroxy-modified polyterpenes, polybutadiene diols, fatty acid-based polyesters or castor oil-based polyesters, preferably hydroxy-modified polyterpenes, in the starting composition. According to the inventor's assessment, these compounds, especially the so-called polyfarnesene in hydroxy-modified polyterpenes, have particularly good damping properties. Corresponding compounds are known to those skilled in the art from the prior art. The following formula (I) shows exemplary diols having a backbone formed from polyfarnesene.

[0070]

[0071] Thus, a preferred method according to the present invention is one in which the starting composition comprises one or more polyol compounds having a backbone made of isoprene units and / or a backbone made of polyterpenes, preferably a backbone made of polyfarnesene, which preferably has a total mass fraction in the range of 5 to 95%, particularly preferably in the range of 10 to 90%, and further particularly preferably in the range of 15 to 80% relative to the mass of the starting composition.

[0072] In order to obtain a crosslinked adhesive having an advantage in terms of sustainable development, the inventor proposes to use bio-based compounds in terms of the diols used, which are very suitable for the method of the present invention and can particularly preferably be combined with bio-based diisocyanates. A preferred method according to the present invention is one in which the first diol compound and / or the second diol compound, preferably the first diol compound and the second diol compound, is prepared from renewable raw materials, wherein the preparation preferably includes the conversion of plant biomass.

[0073] The inventor has found an advantageous method for preparing polyurethane prepolymers, which can be carried out either in a solvent or without a solvent, with the former being preferred. When using a solvent, a preferred method according to the present invention is one in which one or more polyurethane prepolymers can be prepared by reacting a starting composition in a solvent, where the solvent is selected from the group consisting of ketones (such as acetone or butan-2-one), esters (such as ethyl acetate), ethers, amides, hydrocarbons (such as gasoline 60 / 90), toluene, halogenated hydrocarbons, and mixtures of these solvents.

[0074] Whether or not a solvent is used, a preferred method according to the present invention is one in which one or more polyurethane prepolymers are prepared by reacting a starting composition in a temperature range of 0 to 120 °C, preferably 10 to 100 °C, particularly preferably 20 to 80 °C.

[0075] According to the inventor's evaluation, in many cases, it is purposeful to provide a catalyst for the preparation of polyurethane prepolymers. In this regard, a method according to the present invention, for example, lies in that one or more polyurethane prepolymers can be prepared by reacting a starting composition in the presence of a catalyst, where the catalyst is selected from the group consisting of organic bismuth compounds, organic tin compounds, organic zirconium compounds, organic zinc compounds, tertiary amine compounds, morphine-containing compounds, iron salts, and potassium salts.

[0076] During the crosslinking process of the polyurethane prepolymer in method step b), both the radical mechanism of the thiol-ene reaction and the Michael reaction can be used advantageously, whereby the crosslinking chemical reaction can be adjusted specifically according to the respective application requirements. In particular, the radical mechanism can achieve a particularly advantageous pot life and good extrudability, while the Michael reaction can be applied in fields where it is inconvenient to use a radiation source for curing.

[0077] Therefore, according to the inventor's evaluation, a preferred method according to the present invention is first one in which the crosslinking of the polyurethane prepolymer in the prepolymer composition is carried out at least partially, preferably mostly, particularly preferably substantially completely, by the reaction of the C-C double bond of a first diol compound with one or more polyfunctional thiol compounds.

[0078] Here, typical initiator systems can be advantageously used, which are known to those skilled in the art for free radical crosslinking, for example for (meth)acrylate-based systems, in which, according to the inventors' evaluation, radiation-based curing is particularly advantageous, especially in applications in 3D printing. Preferred in this regard is the method according to the invention as follows, wherein one or more initiators are selected from the group consisting of radiation-activated initiators, thermally-activated initiators, and redox initiators, preferably selected from the group consisting of radiation-activated initiators. In this regard, preferred is the method according to the invention as follows, wherein one or more initiator compounds are selected from the group consisting of α-hydroxy ketones, α-alkoxy ketones, α-amino aryl ketones, diaryl ketones, azo compounds, acylphosphine oxides, organic or inorganic peroxides, camphorquinone, and camphorquinone derivatives. As a supplement or alternative, preferred is the method according to the invention as follows, wherein one or more initiator compounds are used, which have a total mass fraction in the range of 0.001% to 5%, preferably in the range of 0.05% to 1%, based on the mass of the polyurethane prepolymer in the prepolymer composition. Those skilled in the art will understand that this relates to the method according to the invention as follows, wherein the prepolymer composition includes the corresponding initiator compound.

[0079] In this regard, the inventors have identified a temperature range within which particularly advantageous results are allowed to be obtained in crosslinking. Preferred in the application of thermally active initiators is the method according to the invention as follows, wherein the crosslinking of the polyurethane prepolymer in the prepolymer composition is carried out in the temperature range of 40 to 300 °C, preferably 50 to 280 °C, particularly preferably 60 to 150 °C. As an alternative, preferred in the application of radiation-activated initiators is the method according to the invention as follows, wherein the crosslinking of the polyurethane prepolymer in the prepolymer composition is carried out in the temperature range of -10 to 40 °C, preferably 10 to 30 °C, particularly preferably 20 to 25 °C.

[0080] Alternatively, according to the inventors' assessment, a preferred method according to the present invention is one in which, by Michael addition, the crosslinking of the polyurethane prepolymer in the prepolymer composition is carried out at least in part, preferably mostly, and particularly preferably substantially completely by reaction of the C-C double bond of a first diol compound with one or more polyfunctional thiol compounds. For this purpose, a preferred method according to the present invention is one in which the crosslinking of the polyurethane prepolymer in the prepolymer composition is catalyzed by one or more catalyst compounds, where the one or more catalyst compounds are selected from the group consisting of bases and nucleophilic compounds, preferably from the group consisting of nucleophilic compounds. In this regard, a particularly preferred method according to the present invention is one in which the one or more catalyst compounds are selected from the group consisting of nitrogen bases such as triethylamine, diisopropylethylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, normal alkylamines, N,N-dimethylpyridin-4-amine or 1H-imidazole, and phosphorus-centered nucleophiles such as trialkylphosphines and alkylarylphosphines such as methyldiphenylphosphine. In terms of the concentration of the catalyst compound, a preferred method according to the present invention is one in which one or more catalyst compounds are used, which have a total mass fraction in the range of 0.001% to 5%, preferably in the range of 0.1% to 1%, relative to the mass of the polyurethane prepolymer in the prepolymer composition. It is also conceivable to use photocatalysts that can be activated by visible light and decomposed into the corresponding bases, for example, a combination of isopropylthioxanthone and triazabicyclodecene tetraphenylborate.

[0081] Although bifunctional thiols can also be used at least in part as polyfunctional thiol compounds, according to the inventors' assessment, it is preferably to use thiols with a higher functionality to achieve a favorable degree of crosslinking. Therefore, a preferred method according to the present invention is one in which the one or more polyfunctional thiol compounds are selected from the group consisting of thiol compounds having two or more, preferably three or more, particularly preferably two or three, and most preferably three thiol groups.

[0082] In this regard, the inventors have successfully determined particularly advantageous thiol compounds and concentration ranges particularly suitable for using them. In this regard, a preferred method according to the invention is one in which one or more polyfunctional thiol compounds are selected from the group consisting of ethylene glycol bis(3-mercaptopropionate), pentaerythritol tetra(2-mercaptoacetate), trimethylolpropane tris(2-mercaptoacetate), ethylene glycol dimercaptoacetate, 1,1,1-trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), 2,2′-(ethylenedioxy)diethanethiol, tetra(ethylene glycol)-dithiol, ethoxylated trimethylolpropane tris(3-mercaptopropionate) and polycaprolactone tetra(3-mercaptopropionate). As a supplement or alternative, a preferred method according to the invention is one in which one or more polyfunctional thiol compounds are used, which have a total mass fraction in the range from 0.5% to 10%, preferably in the range from 3% to 6%, relative to the mass of the polyurethane prepolymer in the prepolymer composition. In this regard, it will be readily understood by the person skilled in the art that it relates to a method according to the invention in which the prepolymer composition comprises the corresponding polyfunctional thiol compound and optionally present initiator.

[0083] However, with regard to the mass fractions defined above, it should be noted that these mass fractions apply in the case where no reactive diluent is provided in the prepolymer composition. These reactive diluents are preferably polyfunctional olefins and thiol compounds. However, unlike free radical chain polymerization reactions, when using a reactive diluent in a thiol-ene reaction, it is also necessary to increase the amount of the polyfunctional mercapto compound used. A preferred method according to the invention is one in which, during the crosslinking of the polyurethane prepolymer in the prepolymer composition, the C-C double bonds of the first diol compound react at least partially with one polyfunctional thiol compound and one or more unsaturated chain-extending molecules, where the chain-extending molecules are preferably selected from polyfunctional olefins, such as bifunctional olefins, preferably the group consisting of allyl ethers and vinyl ethers. However, in this case, a preferred method according to the invention is one in which one or more polyfunctional thiol compounds are used, which have a total mass fraction in the range from 0.5% to 40%, preferably in the range from 3% to 25%, relative to the mass of the polyurethane prepolymer in the prepolymer composition. However, in this case, a preferred method according to the invention is one in which one or more polyfunctional thiol compounds are used, which have a total mass fraction in the range from 0.5% to 30%, preferably in the range from 3% to 15%, relative to the total mass of the polyurethane prepolymer and the chain-extending molecules in the prepolymer composition.

[0084] It is particularly advantageous according to the inventor's assessment that the crosslinked binder produced also comprises a resin, in particular a tackifying resin (or resin for increasing tack). In this regard, a preferred method according to the invention is one in which the crosslinked binder comprises one or more resins which have a total mass fraction, relative to the mass of the crosslinked binder, of preferably 70% or less, particularly preferably 60% or less and very particularly preferably 50% or less. Examples of such tackifying resins include hydrocarbon resins (such as polymers based on unsaturated C5 or C9 monomers), terpene phenolic resins, polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene, aromatic resins such as coumarone-indene resins or resins based on styrene or α-methylstyrene, and rosin and its derivatives, such as disproportionated, dimerized or esterified resins, such as reaction products with ethylene glycol, glycerol or pentaerythritol.

[0085] However, according to the inventor's assessment, certain polyurethane-based resins are particularly suitable for polyurethane-based crosslinked binders. The inventor has specifically adapted certain polyurethane-based resins to the requirements of the method according to the invention and considers them to be particularly advantageous, especially in relation to the use of 3D printing processes. Accordingly, a particularly preferred method according to the invention is one in which the resin is selected from the group consisting of polyurethane resins. Of course, the polyurethane resins mentioned here are not the polyurethane prepolymers or crosslinked polyurethane polymers in the method of the present invention; on the contrary, the polyurethane resins are different from them. Obviously, the polyurethane resins are incorporated or added to the crosslinked binder prepared by the method according to the invention.

[0086] Particularly preferred is a method according to the invention in which the polyurethane resin can be prepared by the reaction of a resin starting composition comprising:

[0087] i) one or more diisocyanate components, and

[0088] ii) one or more polyol components, preferably diol components.

[0089] In this regard, it is particularly advantageous according to the inventor's assessment to use monomeric polyols instead of oligomers in the corresponding resin starting composition, so that a high density of polyurethane groups can be obtained. Accordingly, a preferred method according to the invention is one in which the polyol component has a weight-average molar mass M WAt 400 g / mol or less, preferably at 250 g / mol or less. As an alternative or in addition, the method according to the invention is also preferred, wherein the oligomer and the polyol component have a total mass fraction of 10% or less, preferably 5% or less, particularly preferably 1% or less, and most particularly preferably 0.1% or less, based on the mass of the resin starting composition. As an alternative or in addition, the method according to the invention is correspondingly preferred, wherein the polyol component is a monomeric polyol component.

[0090] Furthermore, preferred is the method according to the invention, wherein the polyol component is not a first diol compound. In this regard, particularly preferred is the method according to the invention, wherein the polyol component does not include terminal C-C double bonds, preferably substantially does not include C-C double bonds.

[0091] Preferred is the method according to the invention, wherein the resin, preferably a polyurethane resin, has a weight-average molar mass M measured by GPC W in the range between 300 and 4000 g / mol, preferably between 500 and 1500 g / mol. As an alternative or in addition, the method according to the invention is also preferred, wherein the resin, preferably a polyurethane resin, has a glass transition temperature measured by DSC of -20 °C or higher, preferably 0 °C or higher. As an alternative or in addition, the method according to the invention is still preferred, wherein the resin, preferably a polyurethane resin, is semi-crystalline or amorphous.

[0092] Regarding the selection of the diisocyanate component, preferably, the method according to the present invention is as follows. One or more diisocyanate components are selected from hexamethylene diisocyanate, 1,6 - diisocyanate - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S)-ethyl 2,6 - diisocyanatohexanoate, (R)-ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane), 4,4'-methylenebis(phenyl isocyanate), toluene - 2,4 - diisocyanate, naphthalene - 1,5 - diisocyanate, and meta - tetramethylxylylene diisocyanate, preferably selected from the following group: hexamethylene diisocyanate, 1,6 - diisocyanate - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S)-ethyl 2,6 - diisocyanatohexanoate, (R)-ethyl 2,6 - diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4 - isocyanatocyclohexane), and 4,4'-methylenebis(phenyl isocyanate). In order to obtain a polyurethane resin with good biodegradability, which is excellently suitable for combination with cross - linked polyurethanes of corresponding designs, the method according to the present invention is particularly preferred according to the inventor's evaluation as follows. One or more diisocyanate components are selected from the group consisting of hexamethylene diisocyanate, 1,6 - diisocyanate - 2,2,4 - trimethylhexane, pentamethylene diisocyanate, (S)-ethyl 2,6 - diisocyanatohexanoate, and (R)-ethyl 2,6 - diisocyanatohexanoate. Regarding the polyol component, preferably, the method according to the present invention is as follows. One or more polyol components are selected from the group consisting of 2 - ethyl - 1,3 - hexanediol, 2 - methyl - 2,4 - pentanediol, 2,2,4 - trimethyl - 1,3 - pentanediol, 2 - methyl - 1,3 - propanediol, 2 - butyl - 2 - ethyl - 1,3 - propanediol, 1,3 - butanediol, 1,4 - butanediol, 3 - methyl - 1,5 - pentanediol, 2,2 - dimethyl - 1,3 - propanediol, 1,2 - propanediol, 2,4 - pentanediol, tripropylene glycol, polyethylene glycol Mn200, and polyethylene glycol Mn300, preferably selected from the group consisting of 2 - ethyl - 1,3 - hexanediol and 2 - methyl - 2,4 - pentanediol.

[0093] In terms of the specific composition of the resin starting composition, a preferred method according to the present invention is one in which the resin starting composition comprises one or more diisocyanate components having a total mass fraction in the range of 30% to 70%, preferably in the range of 40% to 60%, and particularly preferably in the range of 45% to 55% relative to the mass of the resin starting composition. As an alternative or in addition, a preferred method according to the present invention in this regard is one in which the resin starting composition comprises one or more polyol compounds having a total mass fraction in the range of 30% to 70%, preferably in the range of 40% to 60%, and particularly preferably in the range of 45% to 55% relative to the mass of the resin starting composition.

[0094] According to the inventors' assessment, similar to the previous description, the advantage for the preferably used polyurethane resin is that, in addition to diols and diisocyanates, monofunctional alcohols or isocyanates are also used in the resin starting composition. Correspondingly, a preferred method according to the present invention is one in which the resin starting composition comprises one or more monofunctional compounds selected from the group consisting of monofunctional alcohols and monofunctional isocyanates, which preferably have a total mass fraction of 10% or more, preferably 15% or more, and particularly preferably 20% or more relative to the mass of the resin starting composition, and / or a total amount in the range of 0.5*[B] to 1.5*[B], preferably 0.8*[B] to 1.2*[B], and particularly preferably 0.95*[B] to 1.05*[B], where [B] is the total amount of terminal OH groups or isocyanate groups of the polyurethane resin, and [B] can be measured or estimated using typical simulation methods to set this characteristic for, for example, a reference sample.

[0095] An advantage of the method according to the present invention can be that, in addition to the resin and especially the polyurethane resin, other components can be added, which can be added to the prepolymer composition and are accordingly included in the crosslinked binder. The benefit of this is that the physico-chemical properties of the crosslinked binder can be made particularly suitable for the corresponding application requirements. An exemplary method according to the present invention is one in which the crosslinked binder comprises one or more other components, where the other components are selected from the group consisting of rheological additives, stabilizers, antioxidants, and colorants, and the total mass fraction of the other components is preferably in the range of 0.1 to 30%, more preferably in the range of 0.5 to 20%, and particularly preferably in the range of 1 to 20% based on the mass of the crosslinked binder.

[0096] Taking into account the subsequent processing of the crosslinked binder, the crosslinked binder is preferably implemented as a pressure-sensitive adhesive, which can be achieved especially by adding a resin, and it is highly particularly preferred to add the above-mentioned polyurethane resin. Correspondingly, a preferred method according to the present invention is one in which the crosslinked binder is preferably a pressure-sensitive adhesive.

[0097] According to professional understanding, a pressure-sensitive adhesive is an adhesive with adhesive properties, that is, it can form a strong bond with an adherend even under relatively low contact pressure. Such pressure-sensitive tapes can generally be re-peeled from the adherend with substantially no residue after use, and generally have permanent tack even at room temperature, which means they have a certain viscosity and contact tack, so they can wet the surface of the substrate even under low contact pressure. The pressure-sensitive tack of the pressure-sensitive tape comes from the use of a pressure-sensitive adhesive as the adhesive. Without wishing to be bound by this theory, it is generally assumed that a pressure-sensitive adhesive can be regarded as a liquid with an extremely high viscosity having an elastic component, and thus has unique viscoelastic properties, resulting in the above-mentioned permanent inherent tack and pressure-sensitive tack. It is assumed that during the mechanical deformation process, a viscous flow process and the establishment of an elastic restoring force will occur in the corresponding pressure-sensitive adhesive. A certain proportion of viscous flow enables adhesion, while a certain proportion of elastic restoring force is necessary to achieve cohesion. The relationship between rheology and pressure-sensitive tack is known in the prior art, for example, it is described in "Satas, Handbook of Pressure Sensitive Adhesives Technology", 3rd Edition (1999), pages 153 to 203. The storage modulus (G') and loss modulus (G'') can be determined by dynamic mechanical analysis (DMA), for example, using a rheometer, as described in WO2015 / 189323, and are generally used to characterize the degree of elastic and viscous content. In the present invention, the following adhesives are preferably considered to have pressure-sensitive tack and are considered pressure-sensitive adhesives, that is, at a temperature of 23 °C and a deformation frequency range of 10 0 to 10 1 radians per second, G' and G'' are each at least partly in the range of 10 3 to 10 7 Pa.

[0098] A special case of other components for adjusting the properties of crosslinked adhesives is insoluble fillers, which can be added to the prepolymer composition to obtain a filled crosslinked adhesive after crosslinking. These insoluble fillers are, for example, particulate fillers with an average particle diameter (D50) of 5 µm or more, preferably 10 µm or more, and particularly preferably 20 µm or more. They are insoluble in the prepolymer composition and thus exist in the prepolymer composition in the form of a dispersion, or are macroscopic fillers such as fibers. Preferably, the insoluble fillers are selected from the group consisting of particulate fillers. Particularly preferably, the insoluble fillers are selected from expandable hollow polymer spheres, non-expandable hollow polymer spheres, solid polymer spheres, hollow glass spheres, solid glass spheres, hollow ceramic spheres, solid ceramic spheres, solid carbon spheres, and powdered inorganic compounds. However, fibers, fabrics, sheets, and rods made of materials insoluble in the prepolymer composition can also be used as insoluble fillers. Since they sometimes have macroscopic dimensions and are insoluble, they generally do not have a significant impact on the relationship between the above prepolymer composition and the crosslinking chemical reaction. Therefore, in the present invention, these insoluble fillers are not included in the prepolymer composition, and they are not considered when calculating the mass fraction relative to the mass of the prepolymer composition. It is stipulated within the scope of the present invention that adding insoluble fillers to the prepolymer composition results in a filled prepolymer composition. Therefore, in this case, a method according to the present invention is involved, wherein the prepolymer composition is a filled prepolymer composition, including:

[0099] aa.1) a prepolymer composition, and

[0100] aa.2) one or more insoluble fillers,

[0101] wherein, based on the mass of the prepolymer composition, the total mass fraction of the insoluble fillers is preferably in the range of 0.1 to 20%, particularly preferably in the range of 0.5 to 15%, and most particularly preferably in the range of 1 to 10%.

[0102] The method according to the present invention can be used not only for the production of tapes but also for 3D printing processes to produce more complex three-dimensional adhesive structures. Nevertheless, the production of tapes is still of great industrial significance.

[0103] Therefore, the present invention mainly also relates to a method for producing a tape, including the method steps of preparing a crosslinked adhesive according to the present invention, and, before or during method step b), preferably before method step b):

[0104] b1a) forming a prepolymer layer composed of the prepolymer composition on a carrier layer or a release layer.

[0105] Here, the term "tape" is clear to a person skilled in the art of adhesion technology. In the present invention, the term "tape" refers to all thin and flat structures, i.e., structures mainly extending in two dimensions, in particular films, film parts and labels, preferably tapes with an extended length and a limited width and corresponding tape parts.

[0106] The material dosage (coating thickness) of the prepolymer composition is preferably between 10 and 1000 g / m 2 and preferably between 15 and 500 g / m 2 and particularly preferably between 20 and 100 g / m 2 between.

[0107] Generally, in order to achieve particularly advantageous results especially in terms of obtaining the best possible operating performance, the crosslinkable adhesive according to the invention is used as an adhesive layer of a single-sided or double-sided tape, which tape further comprises a carrier layer; or the adhesive layer is arranged on a release layer, such as a backing, and the adhesive layer can be easily peeled off from the release layer.

[0108] In this regard, the following method for preparing a tape is preferred, in which a prepolymer layer is formed on a release layer. In this regard, the following method for preparing a tape is preferred, in which the release layer consists of one or more materials selected from polyethylene, polypropylene, polyethylene terephthalate, paper and combinations of these materials, and the release material is preferably coated on one or both sides, particularly preferably on both sides, with a release layer, preferably a urethane or silicone release layer, particularly preferably a silicone release layer, and the silicone release layer is particularly preferably prepared by crosslinking a crosslinkable silicone system comprising one or more polysiloxanes.

[0109] Different from the release layer, the term "carrier layer" generally refers to the layer in a multi-layer tape that plays an important role in determining the mechanical and physical properties of the tape, such as tear resistance, elasticity, insulation or resilience. Common materials for the carrier layer include fabrics, gauzes, papers and plastic films, such as PET films and polyolefin films.

[0110] When adding a carrier layer, it is advantageous to use an adhesion promoter (i.e., a so-called primer layer) between the carrier material and the prepolymer composition or to physically pretreat the carrier surface to improve the adhesion of the crosslinkable adhesive to the carrier material. In the tape with a carrier layer according to the invention, the adhesive layer can be successively covered by a release cover layer, a so-called release liner, to achieve smooth unrolling and protect the adhesive from contamination. Here, in the case of a single-sided tape, the carrier can be provided with a release layer on one side, and the release layer can be silicone-based, urethane-based or acrylate-based, etc.

[0111] However, since the method according to the invention is particularly suitable for 3D printing processes, the invention also particularly relates to a method for producing a crosslinked three-dimensional adhesive structure by means of a 3D printing process, comprising the method steps of the method according to the invention for producing a crosslinked adhesive, and the following method steps before or during method step b), preferably before method step b):

[0112] b1b) shaping the prepolymer composition by means of an application unit of a 3D printing device to form a three-dimensional adhesive structure.

[0113] A person skilled in the art is familiar with a large number of methods for producing three-dimensional target structures using 3D printing devices in the prior art, in particular the so-called material extrusion methods. A person skilled in the art understands that the method according to the invention is basically compatible with various 3D printing devices and 3D printing processes. In this regard, a method for producing a 3D adhesive structure is preferred, wherein the production of the 3D adhesive structure is carried out in a melt coating method.

[0114] This 3D printing process mainly comprises producing a 3D adhesive structure from a prepolymer composition, which is crosslinked in method step b) to obtain a crosslinked 3D adhesive structure.

[0115] The inventors propose that the viscosity of the prepolymer composition or its temperature dependence should be specifically optimized when implementing the corresponding 3D printing process in order to obtain particularly advantageous application properties, namely that the prepolymer composition can be applied easily and precisely while at the same time exhibiting sufficient structural integrity to form a 3D adhesive structure and maintain this shape before crosslinking. In this regard, the inventors have successfully determined particularly preferred viscosity ranges, and by adjusting these viscosity ranges, prepolymer compositions that are very suitable for various 3D printing processes (especially the melt coating method) can be obtained. Preferably, the method according to the invention is such that the dynamic viscosity of the prepolymer composition at 25 °C ranges from 500 to 500,000 Pa s, preferably from 1000 to 200,000 Pa s, particularly preferably from 2000 to 100,000 Pa s. As an alternative or supplement, preferably, the method according to the invention is such that the dynamic viscosity of the prepolymer composition at 100 °C ranges from 2 to 2500 Pa s, preferably from 5 to 2000 Pa s, particularly preferably from 10 to 1000 Pa s, and most particularly preferably from 15 to 300 Pa s. In the present invention, the dynamic viscosity is determined according to the DIN 53019-1 standard of 2008; at the corresponding temperature, the shear rate is 1 s -1 .

[0116] Those skilled in the art will understand that the present invention also relates to a crosslinked adhesive which is prepared by using the method for preparing a crosslinked adhesive according to the present invention, or can be prepared by using the method for preparing a crosslinked adhesive according to the present invention.

[0117] Based on the method for preparing a tape or a 3D adhesive structure according to the present invention, products obtained thereby are also disclosed within the scope of the present invention.

[0118] Therefore, first, a tape is disclosed which is prepared by or capable of being prepared by the method for preparing a tape according to the present invention, and includes an adhesive layer composed of the crosslinked adhesive according to the present invention, wherein the adhesive layer is disposed on a carrier layer or a release layer.

[0119] A crosslinked 3D adhesive structure is also disclosed, and the 3D adhesive structure is prepared by or can be prepared by the method according to the present invention, and the 3D adhesive structure includes a three-dimensionally formed crosslinked adhesive according to the present invention.

[0120] Finally, the use of the above-mentioned prepolymer composition is also disclosed, that is, a prepolymer composition containing one or more polyurethane prepolymers, wherein one or more polyurethane prepolymers can be prepared by the reaction of a starting composition, and the starting composition includes:

[0121] i.v) one or more diisocyanate compounds,

[0122] ii.v) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols having at least one C-C double bond / molecule, and

[0123] iii.v) one or more second diol compounds different from the first diol compounds,

[0124] As a printing material in a 3D printing process, especially a hot melt coating process, for generating a 3D adhesive structure, preferably in the method for preparing a crosslinked three-dimensional adhesive structure according to the present invention.

[0125] The present invention and preferred embodiments thereof will be further explained and illustrated below in conjunction with experiments.

[0126] The substances used herein are described in Table 1 below.

[0127]

[0128]

[0129] Samples prepared within the scope of the present invention were analyzed by the following methods. Unless otherwise specified, the measurements were carried out in a test environment of 23 ± 1°C and 50 ± 5% relative humidity.

[0130] Vitrification transition temperature (DSC):

[0131] The vitrification transition temperature (Tg) was determined by differential scanning calorimetry (DSC). For this purpose, approximately 5 mg of the sample was weighed into an aluminum crucible (volume 25 µL), and the crucible was sealed with a perforated lid. Measurements were carried out using a Netzsch DSC Sirius 3500 device under a nitrogen atmosphere. After cooling the sample to -140 °C, it was heated to 150 °C at a heating rate of 10 K / min and then cooled again to -140 °C. For the second heating curve, it was heated to 150 °C again at a rate of 10 K / min. The change in heat capacity was recorded in order to identify the vitrification transition process as a step in the graph. The vitrification transition temperature was analyzed by the conventional method: a tangent was applied to the heat map baseline before and after the step. In the area of the step, a leveling line was drawn parallel to the ordinate so that it intersected the two tangents, thus forming two regions and (between each tangent, the leveling line and the measurement curve) the same area. The intersection of the leveling line positioned in this way with the measurement curve represents the vitrification transition temperature.

[0132] Adhesion

[0133] The adhesion (peel strength) was tested according to PSTC-1. A 2-cm-wide pressure-sensitive tape (consisting of a 23-µm-thick PET film etched with trichloroacetic acid and a pressure-sensitive adhesive film attached thereto) was adhered to the test plate, and a 4-kg roller was rolled on the test plate 5 times. The test plate was clamped, and the self-adhesive tape was pulled out from its free end at a speed of 300 mm / min using a tensile testing machine, with a peel angle of 180°. The required pulling force was measured by a tensile force tester. The measurement results were averaged over three measurements and standardized by the tape width, in units of N / cm. The test plate was a polished steel plate with a thickness of 2 mm.

[0134] Shear strength:

[0135] The shear strength was tested according to PSTC-7. A 1.3-cm-wide self-adhesive tape was adhered to a polished steel disk with a length of 2 cm, and a 2-kg roller was rolled on the steel disk twice. The plate was load-balanced without load for 30 minutes under the test conditions. Then the test weight was connected, a shear load parallel to the bonding surface was applied, and the time before bond failure was measured, in minutes. If a holding time of 10,000 minutes was reached, the test was terminated before bond failure.

[0136] Decomposition characteristics:

[0137] The decomposition characteristics of the polymer were tested under simulated composting conditions in the laboratory according to DIN EN ISO 20200:2016-05 to measure its compostability. Decomposition refers to the physical breakdown of the material into very small fragments. To pass the test, at least 90% of the material must decompose into particles smaller than 2 mm within 6 months. The decomposition test was carried out using commercially available compost soil, namely the tangocomp brand compost soil from VKN-Vertriebsgesellschaft Kompostprodukte Nord mbH in this example. The water content of the compost soil was set at 55% to 60%. To determine the water content, three 10 g samples of the compost soil were first dried at 120 °C for 2 hours, and then the water loss was measured to determine the water content of the soil. The missing water was replenished in the form of chlorine-free tap water.

[0138] When conducting the decomposition test, first, 150 g of compost soil with a water content of 60% was placed in a 1000 ml polyethylene beaker. Then, a sample to be analyzed, approximately 25 cm 2 in size, was placed on the first layer of soil. The sample was an adhesive (layer thickness: 200 µm), which was applied to a 25 µm thick cellophane film (a carrier material with known degradation properties) during the test. A second layer of 150 g of compost soil of the same weight was placed on the sample. The PE cup was covered with a lid. To aerate the compost, two holes with a diameter of 2.0 mm each were pre-drilled in the lid. The samples prepared in this way could be stored at 60 ± 2 °C for up to 180 days, and water was added every 3 - 4 days to compensate for the water loss. After 12 weeks, the decomposition progress of the samples was visually evaluated.

[0139] The decomposition characteristics of all samples were qualitatively evaluated. Then, the results were classified according to the degree of decomposition after 12 weeks as follows:

[0140] (+) More than 90% of the samples decomposed into particles smaller than 2 mm;

[0141] (o) 50% to 90% of the samples decomposed into particles smaller than 2 mm; and

[0142] (-) Less than 50% of the samples decomposed into particles smaller than 2 mm.

[0143] Impact resistance (DuPont test)

[0144] For the impact resistance test, transfer tapes were fabricated with a thickness of 50 µm for each tape's adhesive film. The samples were cut into a square frame shape (outer width: 33 mm x 33 mm; tab width: 2 mm; inner dimension (window opening): 29 mm x 29 mm) using a laser cutter. Then the samples were adhered to a polycarbonate (PC) window (35 mm x 35 mm, thickness: 3 mm). On the other side of the transfer tape, a polycarbonate frame (outer width: 45 mm x 45 mm; tab width: 10 mm; inner dimension (window cutout): 25 mm x 25 mm; thickness: 3 mm) was pasted. The bonding area was 248 mm 2 . The bonding part was completed such that the geometric centers and diagonals were respectively superimposed on each other (corner to corner). Then the bonding part was pressed with a pressure of 248 N for 5 seconds and stored for 24 hours.

[0145] The assembly of the PC frame, tape, and PC window was tensioned in a sample holder to keep the protruding edges of the frame flat. The assembly was horizontally oriented. The window was pasted under the PC frame and fixed only by the bonding connection ("free floating"). Then the specimen holder was inserted into the predetermined frame of a "DuPont impact tester". An impact head (weight: 150 g) was inserted so that the circular impact geometry with a diameter of 24 mm was centered and flush with the freely accessible surface of the PC window from above. A weight guided by two guide rods was dropped vertically from a height of 5 cm. The height of the weight drop was increased in 5 cm increments until the applied impact energy broke the bonding connection and the PC window detached from the PC frame. Five measurements were made for each sample, and then the average value was determined.

[0146] To make different samples comparable, the energy (E) was calculated as follows: E [J] = height [m] * object weight [kg] * 9.81 kg / m*s 2 .

[0147] A. Preparation of polyurethane prepolymer:

[0148] The polyurethane prepolymer was prepared using the solvents of the components listed in Table 2. Additionally, the polyurethane prepolymer can also be prepared without solvent.

[0149] In each case, the method for preparing the polyurethane prepolymer was to put the solvent, all the first and second diol compounds, and (if necessary) other polyols and catalysts into a reaction vessel. The mixture was homogenized using a laboratory mechanical stirrer in an inert gas environment. Diisocyanate was added, and the mixture was stirred for 1.5 hours in an inert gas environment at room temperature. Then the mixture was stored in a heating cabinet at 40°C for 48 hours to complete the reaction.

[0150]

[0151] B. Preparation of the Adhesive

[0152] A crosslinked adhesive is prepared from the polyurethane prepolymer prepared below point A.

[0153] An initiator and the polyfunctional thiol compound shown in Table 3 are added to the polyurethane prepolymer, and the mixture is homogenized for at least 5 minutes. For the production of the tape, the mixture is coated on a carrier made of etched PET film or a PET liner coated with a silicone release agent using a laboratory coater. The solvent is evaporated for 15 minutes in a convection oven at 80 °C (etched PET film) or 60 °C (PET liner coated with a silicone release agent). The dried film is covered with a silicated PET film. In the case of using a photoinitiator, the uncrosslinked film is irradiated with an ultraviolet light source compatible with the initiator (dose: 1800 - 2400 mJ / cm 2 ). A crosslinked adhesive film with a layer thickness of 25 - 30 microns (unless otherwise specified) can be obtained. However, in principle, crosslinking can also be carried out using the thiol-Michael reaction.

[0154] The crosslinking of reference PSA13 is carried out using a polyisocyanate.

[0155]

[0156] a) The silicated PET film of PSA10 is removed before crosslinking in order to achieve crosslinking under the influence of oxygen.

[0157] The performance of the tapes produced at points A and B is tested using the above method. The results obtained are summarized in Table 4.

[0158]

[0159] The test results listed in Table 4 show that excellent pressure-sensitive adhesives can be obtained using another crosslinking chemistry method according to the method of the present invention, and this method can meet the various application requirements of those skilled in the art. In particular, favorable adhesion, shear life, and impact resistance can be obtained through this method. In addition, pressure-sensitive adhesives with good decomposition characteristics can also be obtained using the method of the present invention.

[0160] Here, a pressure-sensitive adhesive with advantageous properties can be obtained in an advantageous manner without exhibiting the disadvantages of crosslinking processes known in the prior art during the manufacturing process, thereby minimizing in particular the risk of contact with or release of isocyanate compounds. The corresponding preparation method is highly tolerant to changing environmental conditions and also to the presence of additives that may act on hydroxyl or isocyanate groups. Since radiation activation can be carried out, the preparation process is very safe to use and can be carried out in a time- and cost-saving manner.

[0161] Furthermore, the comparison between PSA9 and PSA10 shows that even when crosslinked under the influence of oxygen, no negative effects are detected, which further demonstrates the robustness of the method according to the invention, especially compared to methods known in the prior art and to processes based on direct radical conversion of terminal C-C double bonds.

[0162] D. Preparation of polyurethane resins

[0163] Advantageous polyurethane resins for the crosslinked adhesives according to the invention were prepared with the components listed in Table 5. In each case, the method for preparing the polyurethane resin is to place the solvent, all polyol components, and the catalyst in a reaction vessel (a solvent-free preparation method can of course also be used). The mixture is homogenized using a laboratory mechanical stirrer in an inert gas environment. The diisocyanate component is added and the mixture is stirred for 1.5 hours in an inert gas environment at room temperature. Then the mixture is stored in a heating cabinet at 40 °C for 48 hours to complete the reaction. The obtained polyurethane resin can be used in solvent form or in solvent-free form.

[0164]

[0165] Based on tests carried out by the inventors using a non-inventive crosslinked pressure-sensitive adhesive (crosslinked directly with free radicals via a first diol compound), it is expected that specific polyurethane resins, when used in combination with the crosslinked adhesives produced according to the invention, will have excellent adhesive properties, especially advantageous finger tack and good adhesive strength, without compromising the degradation properties, especially compared to established resins such as terpene-phenolic resins or hydrogenated rosin resins.

[0166] E. 3D printing of adhesives:

[0167] Based on the inventors' experiments on non-inventive crosslinked pressure-sensitive adhesives (crosslinked directly with free radicals via a first diol compound), it was demonstrated that specific polyurethane prepolymers and crosslinking chemical reactions controlled by the first diol compound are very suitable for 3D printing.

[0168] In this experiment, the corresponding polyurethane prepolymer was prepared solvent-free and transferred into the printing cartridge without air bubbles. 3D printing tests were successfully carried out using an X400 printer from InnovatiQ. The feed temperature during printing was 90 °C, so that an extrusion temperature of at least 70 °C could be ensured. At an extrusion pressure of 2.5 bar, the desired circular geometry could be printed onto a plastic plate using a nozzle with a width of 0.4 mm operating according to the endless piston principle. The non-crosslinked binder was irradiated with an ultraviolet light source matching the initiator (dose: 1800 - 2400 mJ / cm 2 ) to crosslink the binder in the previously generated geometry.

Claims

1. A method for preparing a crosslinked binder, especially within the scope of a 3D printing process, the method comprising the method steps: a) Prepare a prepolymer composition comprising one or more polyurethane prepolymers, wherein, The one or more polyurethane prepolymers can be prepared by the reaction of a starting composition, the starting composition comprising: i) one or more diisocyanate compounds, ii) one or more first diol compounds, where the first diol compounds are selected from the group consisting of diols having at least one C-C double bond / molecule, and iii) one or more second diol compounds different from the first diol compounds, and b) Crosslinking the polyurethane prepolymer in the prepolymer composition by the reaction of the C-C double bond of the first diol compound with one or more polyfunctional thiol compounds to obtain a crosslinked polyurethane polymer.

2. The method according to claim 1, wherein The total mass fraction of the one or more diisocyanate compounds comprised in the starting composition relative to the mass of the starting composition is from 1% to 30%.

3. The method according to claim 1 or 2, wherein The one or more first diol compounds are selected from the group consisting of acrylates, methacrylates and allyl ethers.

4. The method according to any one of claims 1 to 3, wherein The total mass fraction of the one or more first diol compounds comprised in the starting composition relative to the mass of the starting composition is from 0.05% to 20%.

5. The method according to any one of claims 1 to 4, wherein The second diol compound is selected from the group consisting of diols, the weight-average molecular weight Mw of which, as determined by GPC, is in the range of 200 to 6000 g / mol.

6. The method according to any one of claims 1 to 5, wherein The second diol compound is selected from the group consisting of diols having a polymerized isoprene unit backbone and / or diols having a polyterpene backbone.

7. The method according to any one of claims 1 to 6, wherein, The total mass fraction of the one or more second diol compounds comprised in the starting composition relative to the mass of the starting composition is from 50% to 95%.

8. The method according to any one of claims 1 to 7, wherein The crosslinking of the polyurethane prepolymer in the prepolymer composition is effected at least in part by a radical reaction of the C-C double bond of the first diol compound with one or more polyfunctional thiol compounds.

9. The method according to any one of claims 1 to 8, wherein The crosslinking of the polyurethane prepolymer in the prepolymer composition is effected at least in part by reaction of the C-C double bond of the first diol compound with one or more polyfunctional thiol compounds in a Michael addition.

10. The method according to any one of claims 1 to 9, wherein, The crosslinked binder comprises one or more resins, where the resins are selected from the group consisting of polyurethane resins.

11. The method according to any one of claims 1 to 10, wherein The prepolymer composition has a dynamic viscosity in the range of 500 to 500000 Pa·s at 25°C, and / or where the prepolymer composition has a dynamic viscosity in the range of 2 to 2500 Pa·s at 100°C.

12. The method according to any one of claims 1 to 11, wherein The crosslinked binder is a pressure-sensitive binder.

13. A method for preparing a tape, comprising the method steps of the method according to any one of claims 1 to 12, and further comprising the method steps before or during method step b): b1a) Forming a prepolymer layer consisting of the prepolymer composition on a carrier layer or a release layer.

14. A method for forming a crosslinked three-dimensional adhesive structure in a 3D printing process, comprising the method steps of the method according to any one of claims 1 to 12, and further comprising the method steps before or during method step b): b1b) Using an application unit of a 3D printing device to form the prepolymer composition to form a three-dimensional adhesive structure.

15. A crosslinked adhesive which is made or can be made by the method according to any one of claims 1 to 14.

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