Method for producing a cross-linked adhesive compound

Abstract

The invention relates to a method for producing a cross-linked adhesive compound, in particular as part of a 3D printing method, having the steps of: a) producing a prepolymer composition comprising one or more polyurethane prepolymers, wherein the one or more polyurethane prepolymers can be produced by reacting a starting composition, comprising: i) one or more diisocyanate compounds, ii) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols with at least one C-C double bond per molecule, and iii) one or more second diol compounds which differ from the first diol compounds, and b) cross-linking the polyurethane prepolymers in the prepolymer composition by reacting C-C double bonds of the first diol compounds with one or more multi-functional thiol compounds in order to obtain cross-linked polyurethane polymers.

Description

[0001] Process for producing a crosslinked adhesive

[0002] Description

[0003] The invention relates to a method for producing a crosslinked adhesive, in particular within the framework of a 3D printing process, a method based thereon for producing an adhesive tape or a crosslinked three-dimensional adhesive structure in a 3D printing process, and a crosslinked adhesive produced by the method. Also disclosed are a corresponding adhesive tape or a corresponding crosslinked three-dimensional adhesive structure and the use of a prepolymer composition as a printing substance in a 3D printing process for producing a three-dimensional adhesive structure.

[0004] Joining separate elements is one of the central processes in manufacturing technology. Along with other methods such as welding and soldering, bonding—that is, joining using an adhesive—is playing a particularly important role today. An alternative to the use of formless adhesives, such as those applied from a tube, is adhesive tape, whose adhesive effect is based on the adhesive used.

[0005] For numerous technical applications, polyurethanes, in particular, have proven to be high-performance base materials as polymer systems for the production of adhesives, as disclosed, for example, in EP 3155034 A1. These polymeric compounds are usually obtained by polyaddition of polyols with polyisocyanates and typically possess physicochemical properties that make them ideal for use in adhesives for various high-performance applications, particularly in the field of electronic products.In addition to their generally very advantageous adhesive properties, these include, for example, high resistance to light, adverse weather influences and a wide range of chemicals. It is considered particularly advantageous that the physical-chemical properties of polyurethanes can in many cases be specifically adapted to the respective application requirements by selecting the starting materials.

[0006] In the production of polyurethane-based adhesives, the first step is usually the production of so-called polyurethane prepolymers, i.e. polyurethanes whose average molecular weight is set comparatively low by the mixing ratio of the starting materials or the reaction conditions, so that the usually hydroxy-terminated and essentially still meltable polyurethane prepolymers can still be processed well, for example by mixing the

[0007] Polyurethane prepolymers with other components such as adhesive resins, which in particular also enables efficient molding of the resulting, still meltable composition, for example, to form the subsequent adhesive layer of an adhesive tape. The adhesive mass is made from the polyurethane prepolymers or the

[0008] Prepolymer composition is obtained by crosslinking the polyurethane prepolymers, which in the prior art is usually done by crosslinking the hydroxy-terminated polyurethane prepolymers using multifunctional isocyanates.

[0009] Despite the numerous advantages of the polyurethane-based adhesives known from the state of the art, these systems are also perceived as disadvantageous in some aspects.

[0010] Due to the reactivity of the multifunctional isocyanates used, the crosslinking of polyurethane prepolymers known from the prior art is often highly dependent on the prevailing humidity, which can impair the reproducibility of the crosslinking. Furthermore, crosslinking usually requires an additional step in which the multifunctional isocyanate is added, often requiring the use of solvents. However, the addition of the multifunctional isocyanate initiates the crosslinking reaction, which begins to decrease processability and shortens the pot life.At the same time, it is often found that with the classic type of crosslinking it can take a comparatively long time until the desired final degree of crosslinking is achieved, which significantly determines the final mechanical properties of the crosslinked adhesive, whereby with the process known from the state of the art this can easily take longer than two weeks.

[0011] In addition, polyurethane-based adhesives produced by means of crosslinking processes known from the prior art are in many cases disadvantageously limited with regard to the further additives that can be added to the polyurethane prepolymer composition before crosslinking, since in particular hydroxyl groups, for example in resins or plasticizers, can negatively influence crosslinking.

[0012] The aspects described above lead, in particular, to the fact that the polyurethane-based adhesives known from the state of the art are generally not suitable for practical use in additive manufacturing processes, which are also commonly referred to as 3D printing processes. This is often perceived as a disadvantage because these modern manufacturing processes – as in many other industries – also open up many interesting applications in the field of adhesive technology, particularly in the targeted formation of three-dimensional adhesive structures whose shape and dimensions can be precisely tailored to the intended application, which is considered particularly advantageous in the field of electronics manufacturing.

[0013] Processing crosslinked polyurethane-based adhesives suitable for the intended application using 3D printing processes is generally not practical. Therefore, only the meltable polyurethane prepolymers or the corresponding polyurethane prepolymer composition can be molded using a 3D printer. However, the addition of multifunctional isocyanates required for crosslinking cannot realistically be carried out after molding due to handling considerations. At the same time, the multifunctional isocyanate cannot be added too early, so that the onset of crosslinking does not compromise processability at short pot lives.Since the introduction of an already crosslinked adhesive through fluid supply lines is also impractical due to the risk of clogging, the equipment requirements for the 3D printing device would increase significantly, as it would have to achieve the most homogeneous mixing possible of the polyurethane prepolymer composition with the multifunctional isocyanate immediately before molding. In many cases, the required solvent would further complicate use in the 3D printer. Furthermore, cleaning and maintenance costs would increase considerably, as even late mixing would still pose the risk of contamination from overly crosslinked adhesive.

[0014] In addition, most additive manufacturing processes that could be considered for printing polyurethane prepolymer compositions are not carried out under inert gas due to manufacturing costs, especially not in mass production, and the 3D printing devices used are usually not equipped for this. However, the vulnerability of the crosslinking chemistry known from the state of the art would also have a particularly detrimental impact on the reproducibility of print quality, which would be unacceptable, especially for many high-performance applications. Furthermore, the comparatively long curing time required to achieve the desired final degree of crosslinking would, in the inventors' opinion, prevent any meaningful use in additive manufacturing.

[0015] The primary object of the present invention was to eliminate or at least reduce the above-described disadvantages of the prior art.

[0016] In particular, it was the object of the present invention to provide a process for producing a crosslinked polyurethane-based adhesive which results in a crosslinked adhesive which has the advantages of polyurethane-based adhesives without the disadvantages of the crosslinking processes known from the prior art becoming apparent during production.

[0017] It was a supplementary object of the present invention that the method to be specified should show good reproducibility even under changing environmental conditions and, in addition, a higher tolerance for the use of different additives.

[0018] In addition, it was a further object of the present invention that the process to be specified should allow the production of crosslinked adhesives with excellent adhesive properties.

[0019] Furthermore, it was an object of the present invention that the process to be specified should enable the production of crosslinked adhesives in a particularly time- and cost-efficient manner, with a particular aim of improving the curing times until the final degree of crosslinking is achieved. It was desirable that the process nevertheless offer particularly high process reliability.

[0020] It was also an object of the present invention that the production of crosslinked adhesives in the process to be specified should be advantageous from the point of view of environmental and occupational safety, in particular the risk of exposure to or release of isocyanate compounds and the need for solvents should be reduced.

[0021] Likewise, it was an object of the present invention that the process to be specified should enable the production of crosslinked adhesives with advantageous biodegradability.

[0022] Furthermore, it was an object of the present invention that the process to be specified should enable the production of crosslinked adhesives with improved damping properties.

[0023] In particular, it was an object of the present invention that the method to be specified should enable the efficient production of the crosslinked adhesive mass even within the framework of a 3D printing process, thus enabling the 3D printing of adhesive structures from polyurethane-based adhesive masses. It was desirable that the method to be specified should place as few equipment requirements as possible on the 3D printing devices used.

[0024] It was an object of the present invention to provide a crosslinked adhesive mass which can be produced by the process to be specified and which has the advantages of polyurethane-based adhesive masses, but can be produced in a particularly time- and cost-efficient manner and with a high level of reproducibility.

[0025] It was a supplementary object of the present invention to provide two processes for producing adhesive tapes and three-dimensional adhesive structures based on the process to be specified. A secondary object of the present invention was also to provide the corresponding adhesive tapes and three-dimensional adhesive structures resulting from these processes.

[0026] Furthermore, it was a secondary object of the present invention to provide a use for a polyurethane prepolymer composition as a printing substance in a 3D printing process for producing a three-dimensional adhesive structure.

[0027] The inventors of the present invention have now found that the objects described above can surprisingly be achieved if, in the production of adhesives, polyurethane prepolymers are used in the prepolymer composition which not only consist of diisocyanate compounds and conventionally used diol compounds, but which also contain CC double bonds in their polymer chain, which are deliberately introduced by the polymerization of unsaturated diols having at least one CC double bond, and if the polyurethane prepolymers are subsequently crosslinked by thiol click chemistry, ie the reaction with one or more multifunctional thiol compounds, as defined in the claims.

[0028] The inventors have found that, surprisingly, the process according to the invention makes it possible to obtain crosslinked adhesives that have the advantages of polyurethane-based adhesives, particularly with regard to their excellent adhesive properties, without the disadvantages of the crosslinking chemistry known from the prior art becoming apparent during production. In particular, susceptibility to atmospheric humidity is reduced, and the use of additives containing hydroxyl groups is also facilitated. Crosslinking by reacting the CC double bonds of the polyurethane prepolymers with one or more multifunctional thiol compounds, which can be initiated, for example, by radiation, also solves the problem of excessively short pot lives, particularly in the case of radiation activation, and allows time- and cost-efficient crosslinking with very short curing times.Furthermore, it is advantageous to avoid the use of isocyanates during crosslinking and, if necessary, to carry out the crosslinking step solvent-free. Compared to an alternative approach in which polyurethane prepolymers are converted to crosslinked polyurethanes via terminal double bonds without the use of multifunctional thiol compounds by radical polymerization, not only does a broader range of possible activation mechanisms become accessible, but the susceptibility of the crosslinking reaction to oxygen can also be further reduced, especially when using a thiol-Michael addition.

[0029] The process according to the invention enables, in particular, the efficient production of three-dimensional adhesive structures from crosslinked polyurethane-based adhesives by means of 3D printing. The equipment requirements for the 3D printing device are minimal, since, for example, only a radiation source for radiation-activated crosslinking needs to be provided, with crosslinking also being possible downstream. The process according to the invention also makes it possible, in particular, to obtain crosslinked adhesives with advantageous biodegradability.

[0030] Furthermore, the inventors have discovered that the specific process surprisingly results in a crosslinked adhesive that exhibits surprisingly improved damping properties compared to conventionally produced crosslinked polyurethane-based adhesives. Without wishing to be bound by this theory, the inventors assume that this is due to the fact that crosslinking in the process according to the invention does not occur via terminal hydroxy groups.It is assumed that, due to the fact that the unsaturated diols with at least one CC double bond are present essentially stochastically in the chain of the polyurethane prepolymers, the crosslinking rather mostly takes place along the polymer chain, whereby a network with a large number of freely movable side chains is obtained, to which the inventors attribute the improved damping properties, whereby this effect can be further enhanced according to the inventors' knowledge if starting substances with side chains are also used in the polyurethane prepolymers, such as diols based on polyfarnesenes or fatty acid esters.

[0031] The above-mentioned objects are thus achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0032] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature of an embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred adhesives, adhesive tapes, three-dimensional adhesive structures, and uses emerge from the features of preferred methods.

[0033] To the extent that both specific amounts or proportions of an element, for example, for the diisocyanate compounds or the first diol compounds, and preferred embodiments of the element are disclosed below, the specific amounts or proportions of the preferably configured elements are also disclosed. Furthermore, it is disclosed that, with the corresponding specific total amounts or total proportions of the elements, at least some of the elements can be preferably configured, and in particular, that preferably configured elements can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

[0034] The invention relates to a process for producing a crosslinked adhesive, in particular within the framework of a 3D printing process, comprising the process steps: a) producing a prepolymer composition comprising one or more polyurethane prepolymers, wherein the one or more polyurethane prepolymers can be produced by reacting a starting composition comprising: i) one or more diisocyanate compounds, ii) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols having at least one CC double bond per molecule, and iii) one or more second diol compounds different from the first diol compounds, and b) crosslinking the polyurethane prepolymers in the prepolymer composition by reacting CC double bonds of the first diol compounds with one or more multifunctional thiol compounds, to obtain crosslinked polyurethane polymers.

[0035] In the process according to the invention, a prepolymer composition is first prepared or provided, which is then crosslinked to obtain the crosslinked adhesive. This prepolymer composition comprises, in addition to the polyurethane prepolymers, the other components that are to be contained in the crosslinked adhesive during the crosslinking process, such as adhesive resins, dyes, or other additives that can be added by a person skilled in the art depending on the intended application. The essential component of the prepolymer composition with regard to the invention are the specific polyurethane prepolymers.

[0036] Polyurethanes per se, as well as the eponymous urethane group and the underlying chemistry, are comprehensively familiar to the skilled person based on their general technical knowledge, with the skilled person also being particularly familiar with the concept of polyurethane prepolymers. The polyurethane prepolymers used in the invention are copolymers that are produced or can be produced by polymerization, more precisely polyaddition, from a specific starting composition. This term expediently also includes compounds that, due to their chain length, could also be referred to as polyurethane pre-oligomers, since the difference between oligomers and polymers is fluid and ultimately arbitrary anyway, so that a distinction is not appropriate in this case.In accordance with the expert understanding and the usual practice in the field of technology, it is expedient to define such copolymers by the manufacturing process or the starting materials used for production, since it is largely impossible to define the corresponding materials in their entirety in any other conclusive way.

[0037] In accordance with this common practice in the field of technology, the manufacturability is stated above with reference to the starting composition, which, in accordance with the expert's understanding, comprises all isolated compounds that are converted into building blocks of the polyurethane prepolymers during polymerization. A corresponding starting composition for the production of copolymers is sometimes also referred to as a monomer composition, although this term is not used in the context of the present invention, since, in particular, many of the typically used diols, e.g., compounds that are suitable as second diol compounds, are themselves, by strict definition, oligomeric or polymeric compounds.In accordance with the understanding of the person skilled in the art, any other components which may be present in the reaction mixture during polymerization but are not incorporated into the polyurethane prepolymers during polymerization, such as solvents or other non-reactive compounds, are not included in the starting composition.

[0038] These components of the starting composition, as defined above, are each used as "one or more" in accordance with the understanding of the person skilled in the art. The term "one or more" refers, in accordance with industry practice, to the chemical nature of the respective compounds and not to their quantity. For example, the starting composition may comprise exclusively hexamethylene diisocyanate as diisocyanate compounds, which would mean that the starting composition comprises a plurality of the respective molecules.

[0039] In accordance with the expert understanding, the prepolymer composition, or more precisely the polyurethane prepolymers, in the prepolymer composition is still uncrosslinked, but can be crosslinked to produce a crosslinked adhesive. The person skilled in the art understands that the term “uncrosslinked” refers to the chemical crosslinking, i.e. the covalent bonding of individual copolymer strands to one another to form a network, and not to any physical crosslinking of the copolymer chains, for example by entanglement, phase separation or crystallization, so that polyurethane prepolymers are generally meltable. The person skilled in the art understands that an uncrosslinked polyurethane prepolymer does not necessarily have to be linear, but can also have branched copolymer chains, which can be the case in particular if the starting composition comprises higher-functionality polyisocyanates and / or polyols in addition to diisocyanates and diols.Even if the transition from branched copolymer chains to a crosslinked network of the crosslinked adhesive may appear blurred in theory, the uncrosslinked state, or crosslinking, is relatively easy for the skilled person to determine in practice. The skilled person can determine this, for example, based on temperature-dependent rheological properties or with simple solubility tests. In crosslinked adhesives, the resulting crosslinked polyurethanes have a greatly increased molecular weight and, as a result, are usually no longer soluble or meltable in organic solvents, so that essentially irreversible liquefaction is only possible through decomposition.

[0040] In this respect, the inventors propose ranges for the average molecular weight of the polyurethane prepolymers which, in the inventors' experience, allow particularly advantageous process configurations to be realized. A process according to the invention is preferred, wherein the one or more polyurethane prepolymers have a weight-average molecular weight M w measured by GPC in the range of 1 .0 x 10 4 up to 8.0 x 10 4 g / mol, preferably in the range of 1.5 x 10 4 up to 6.0 x 10 4 g / mol, particularly preferably in the range of 2.0 x 10 4 up to 4.0 x 10 4 g / mol.

[0041] In the context of the present invention, all information on the weight-average molecular weight M wto the determination by gel permeation chromatography (GPC). The determination is carried out using degassed THF as the mobile phase, 50 pL injection volume, and a sample concentration of 3 g / L at a flow rate of 1 mL / min at 25 °C on a system consisting of a PSS-SECcurity 1260 HPLC pump, a PSS SDV 10 pm ID 8 mm x 50 mm guard column, and a PSS SDV 5 pm 10 3 Ä ID 8 mm x 300 mm, one PSS SDV 5 pm 10 5 Ä ID 8 mm x 300 mm, one PSS SDV 5 pm 10 6 ID 8 mm x 300 mm and a SECcurity differential refractometer (RI) detector. Data are recorded and evaluated using PSS - WinGPC UniChrome version 8.4 software. Calibration is performed using polystyrene standards, which are universally converted to a polystyrene calibration using the Mark Houwink coefficients K and a.

[0042] In the process according to the invention, a crosslinked adhesive is produced from the prepolymer composition by crosslinking the polyurethane prepolymers, which comprises crosslinked polyurethane polymers in addition to any other constituents of the prepolymer composition and their reaction products. The person skilled in the art will understand that, depending on the form of crosslinking or the other constituents of the crosslinked adhesive, these may also be polyurethane copolymers. In the simplest case, the crosslinked polyurethane polymers obtained represent the crosslinked adhesive. However, preference is given to a process according to the invention in which the crosslinked adhesive comprises the crosslinked polyurethane polymers in a combined mass fraction in the range from 30 to 100%, preferably in the range from 40 to 100%, particularly preferably in the range from 50 to 100%, based on the mass of the crosslinked adhesive.

[0043] In the process according to the invention, unlike the prior art, crosslinking is not carried out, or at least not exclusively, preferably not at all, by reaction with multifunctional isocyanates, but rather relies on the so-called thiol-click chemistry.

[0044] The concept of so-called thiol-click chemistry is familiar 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. This thiol-ene reaction generally allows for high yields with good selectivities and fast reaction rates. The thiol-ene reaction can proceed via a radical addition or a catalyzed Michael reaction based on an anionic mechanism.

[0045] However, typical polyurethane prepolymers cannot actually be crosslinked by radical polymerization or an anionic thiol-ene reaction. This is only possible through the CC double bonds, which are incorporated into the specific polyurethane prepolymers by the first diol compounds.

[0046] The inventors have recognized that, with regard to the crosslinking step and the physicochemical properties that can be adjusted in the crosslinked adhesive, it is also important not only to use first diol compounds, but also to use at least one second diol compound by means of which the concentration of units derived from first diol compounds in the polyurethane prepolymers can be controlled, so that the concentration of CC double bonds can be controlled. Those skilled in the art will understand that the expression "different from the first diol compounds" means that the second diol compounds do not fall under the definition of the first diol compounds. Two different diol compounds, which are each, for example, diols with a terminal CC double bond per molecule, will not represent a first and second diol compound within the meaning of the present invention, but rather will be two different first diol compounds.

[0047] The polyurethanes obtained in process step b) are crosslinked, as is the crosslinked adhesive containing these polyurethanes and produced in the process according to the invention. Those skilled in the art will understand that this means that the polyurethane prepolymers were at least partially crosslinked as a result of process step b) necessarily provided for by the invention. In accordance with the understanding of those skilled in the art, this does not require the achievement of the theoretically maximum possible crosslinking in the sense of complete crosslinking of the adhesive, so that any crosslinking carried out during process step b) according to the above-defined criteria is sufficient, and thus even systems in which a crosslinking reaction takes place are considered crosslinked within the meaning of the invention.

[0048] The components used in the starting composition are first described in more detail below. In this respect, the inventors have succeeded in identifying particularly preferred configurations and mass fractions for the individual components, with which advantageous polyurethane prepolymers or high-performance crosslinked adhesives can be obtained in the course of the process according to the invention. In accordance with industry practice, the mass fractions are given as the combined mass fractions of the one or more components, thereby expressing that the mass fraction of the correspondingly configured components taken together meets the corresponding criteria. In the absence of other information, the mass of the starting composition serves as the reference system.

[0049] To obtain crosslinked adhesives with advantageous biodegradability, the inventors believe it is advantageous to use aliphatic compounds as the diisocyanates. Accordingly, a process according to the invention is preferred, wherein the diisocyanate compounds are selected from the group consisting of aliphatic diisocyanates.

[0050] Particularly in cases where biodegradability is not a priority, aromatic diisocyanates can also be used alongside aliphatic diisocyanates, allowing greater flexibility in adjusting the physicochemical properties. However, the inventors believe it is advisable not to choose an excessively high proportion even in these cases.Accordingly, a process according to the invention is preferred, wherein the starting composition contains one or more aromatic polyisocyanate compounds, preferably in a combined mass fraction of 30% or less, particularly preferably 20% or less, very particularly preferably 15% or less, based on the mass of the starting composition and / or wherein the combined mass fraction of aromatic polyisocyanate compounds in the starting composition is 10% or less, particularly preferably 5% or less, very particularly preferably 1% or less, based on the mass of the starting composition.

[0051] With regard to the average molecular weights of the polyurethane prepolymers to be influenced thereby, preference is given to a process according to the invention wherein the starting composition comprises the one or more diisocyanate compounds, preferably the aliphatic diisocyanates, in a combined mass fraction in the range from 1 to 30%, preferably in the range from 4 to 20%, particularly preferably in the range from 5 to 15%, based on the mass of the starting composition.

[0052] In addition, higher-quality polyisocyanates can also be used to adjust the physicochemical properties of the starting composition. However, according to the inventors, the resulting branching of the polyurethane prepolymers should be kept as low as possible.For this purpose, a process according to the invention is preferred, wherein the starting composition comprises one or more polyisocyanate compounds having three or more isocyanate groups, preferably in a combined mass fraction of 10% or less, particularly preferably 5% or less, very particularly preferably 3% or less, most preferably 0.5% or less, based on the mass of the starting composition and / or wherein the combined mass fraction of polyisocyanate compounds having three or more isocyanate groups in the starting composition is 10% or less, particularly preferably 5% or less, very particularly preferably 1% or less, based on the mass of the starting composition.

[0053] In principle, a large number of suitable diisocyanate compounds are known to the person skilled in the art. However, in the opinion of the inventors, a process according to the invention is preferred, wherein the one or more diisocyanate compounds are selected from the group consisting of hexamethylene diisocyanate, 1,6-diisocyanato-2,2,4-trimethylhexane,

[0054] Pentamethylene diisocyanate, (S)-ethyl 2,6-diisocyanatohexanoate, (F?)-ethyl 2,6-diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4-isocyanatocyclohexane), 4,4'-methylenebis(phenyl isocyanate), toluene-2,4-diisocyanate, naphthylene-1,5-diisocyanate and meta-tetramethylxylylene diisocyanate, preferably selected from the group consisting of hexamethylene diisocyanate, 1,6-diisocyanato-2,2,4-trimethylhexane,

[0055] Pentamethylene diisocyanate, (S)-ethyl 2,6-diisocyanatohexanoate, (F?)-ethyl 2,6-diisocyanatohexanoate, isophorone diisocyanate, 1,1'-methylenebis(4-isocyanatocyclohexane), and 4,4'-methylenebis(phenyl isocyanate). To obtain a crosslinked adhesive with good biodegradability, the inventors believe that processes according to the invention are particularly preferred, wherein the 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 (F?)-ethyl 2,6-diisocyanatohexanoate. Additionally or alternatively, a process according to the invention is preferred, wherein the diisocyanate compounds are selected from the group consisting of diisocyanates having two or more, preferably three or more, alkyl groups, preferably methyl groups, along the main chain.

[0056] In the opinion of the inventors, the use of rather short diisocyanate compounds and thus a process according to the invention is preferred, wherein the one or more diisocyanate compounds are selected from the group consisting of aliphatic diisocyanates having 3 to 20, preferably 4 to 18, particularly preferably 5 to 15, C atoms.

[0057] To obtain a crosslinked adhesive composition that is advantageous in terms of sustainability, the inventors propose using bio-based diisocyanate compounds that are advantageously suitable for the process according to the invention. Accordingly, a process according to the invention is preferred in which the one or more diisocyanate compounds are produced from renewable raw materials, with the production preferably comprising the conversion of plant biomass.

[0058] According to the inventors, a particular advantage of the present invention is that no terminal hydroxyl groups are required for subsequent crosslinking. This makes it possible to use monofunctional alcohols or isocyanates in the starting composition in addition to the diols and diisocyanates. These monofunctional building blocks terminate the polymer chains obtained by polymerization and thus advantageously allow for efficient adjustment of the desired average molecular weight. Furthermore, the use of these monofunctional compounds makes it possible to obtain polyurethane prepolymers that bear neither hydroxyl groups nor isocyanate groups at their ends, which is particularly preferred with regard to the storage stability of the polyurethane prepolymers.Accordingly, a process according to the invention is preferred, wherein the starting composition comprises one or more monofunctional compounds selected from the group consisting of monofunctional alcohols and monofunctional isocyanates, preferably in a combined mass fraction of 0.1% or more, preferably 1% or more, particularly preferably 3% or more, based on the mass of the starting composition and / or in a combined amount of substance in the range from 0.5*[A] to 1.5*[A], preferably in the range from 0.8*[A] to 1.2*[A], particularly preferably in the range from 0.95*[A] to 1.05*[A], where [A] is the combined amount of substance of the terminal OH groups or isocyanate groups of the polyurethane prepolymers, where [A] can be determined, for example, on reference samples by measurement or estimated using typical simulation methods to adjust this feature.

[0059] In the inventors' opinion, the first diol compounds should preferably be designed to be relatively short in order to obtain particularly advantageous polyurethane prepolymers or advantageous crosslinked adhesives. As a result, the first diol compounds not only incorporate the double bonds required for crosslinking into the polyurethane prepolymers, but also achieve a relatively high density of urethane groups in the polyurethane (pre)polymers. The high density of structurally comparatively rigid functional groups and the formation of hydrogen bonds produce so-called hard blocks, which advantageously increase the adhesive properties of the crosslinked adhesive. Against this background, preference is initially given to a process according to the invention wherein the first diol compounds are selected from the group consisting of diols having 4 to 60, preferably 5 to 30, particularly preferably 6 to 10, carbon atoms.Additionally or alternatively, a process according to the invention is preferred, wherein the first diol compounds are selected from the group consisting of diols having a molecular weight in the range from 70 to 750 g / mol, preferably in the range from 100 to 500 g / mol, particularly preferably in the range from 140 to 250 g / mol.

[0060] Particularly preferred is a process according to the invention wherein the one or more first diol compounds are selected from the group consisting of diols having exactly one CC double bond per molecule. Additionally or alternatively, preferred is a process according to the invention wherein the one or more first diol compounds are selected from the group consisting of diols having at least one, preferably exactly one, terminal CC double bond per molecule. Additionally or alternatively, preferred is also a process according to the invention wherein the one or more first diol compounds are selected from the group consisting of aliphatic diols.

[0061] According to the inventors' assessment, (meth)acrylates, allyl ethers, and diols having at least one alkenyl radical are particularly suitable as first diol compounds, with monomeric compounds being preferred in each case. Accordingly, a process according to the invention is preferred, wherein the one or more first diol compounds are selected from the group consisting of acrylates, methacrylates, allyl ethers, vinyl ethers, and diols having at least one alkenyl radical, preferably selected from the group consisting of methacrylates and allyl ethers.

[0062] Substantially independent of the specific selection of the first diol compounds, a process according to the invention is preferred wherein the starting composition comprises the one or more first diol compounds in a combined mass fraction in the range of 0.05 to 20%, preferably in the range of 0.5 to 6%, particularly preferably in the range of 1 to 3.5%, based on the mass of the starting composition.

[0063] However, with regard to crosslinking kinetics, the resulting adhesive properties, and the possibility of achieving favorable biodegradability, the inventors consider it preferable to largely avoid the use of monomeric diols that contain multiple groups that can be converted in a thiol click reaction. In particular, it is advantageous to keep the content of monomeric second diols with two or more CC double bonds per molecule, especially with two or more terminal CC double bonds, relatively low.Accordingly, a process according to the invention is preferred, wherein the starting composition comprises one or more diols, preferably monomeric diols, having two or more CC double bonds per molecule, preferably in a combined mass fraction of 30% or less, particularly preferably 20% or less, very particularly preferably 10% or less, based on the mass of the starting composition and / or wherein the combined mass fraction of diol compounds having two or more CC double bonds per molecule in the starting composition is 10% or less, particularly preferably 5% or less, very particularly preferably 1% or less, based on the mass of the starting composition.

[0064] It can be seen as an advantage of the present invention that it is very flexible with regard to the other diols, i.e., the second diol compounds, and thus enables flexible adaptation of the physicochemical properties to the respective required requirement profile. Those skilled in the art will understand that the second diol compounds preferably differ from the first diol compounds in that they do not contain any CC double bonds, so that they are saturated diol compounds. Thus, a process according to the invention is preferred wherein the second diol compounds are selected from the group consisting of saturated diols.

[0065] In principle, the second diol compounds can be either comparatively short molecules, so-called chain extenders, or oligomeric or polymeric diols, and these can also be mixed. In the opinion of the inventors, the use of oligomeric and polymeric diol compounds is particularly advantageous. Against this background, a process according to the invention is preferred for certain applications, wherein the one or more second diol compounds are selected from the group consisting of saturated diols having 5 to 600, preferably 8 to 350, particularly preferably 10 to 250, carbon atoms. However, a process according to the invention is particularly preferred, wherein the one or more second diol compounds are selected from the group consisting of diols having a weight-average molar mass M wmeasured by GPC in the range of 200 to 6000 g / mol, preferably in the range of 300 to 4500 g / mol, particularly preferably in the range of 400 to 3000 g / mol.

[0066] In the case of oligomeric or polymeric second diol compounds, compounds present as amorphous or semicrystalline substances are particularly preferably used. A process according to the invention is preferred in which the second diol compounds are selected from the group consisting of amorphous or semicrystalline, preferably amorphous, diol compounds.

[0067] Substantially independent of the specific selection of the second diol compounds, a process according to the invention is preferred, wherein the starting composition comprises the one or more second diol compounds in a combined mass fraction in the range from 50 to 99%, preferably in the range from 60 to 97%, particularly preferably in the range from 70 to 95%, based on the mass of the starting composition. However, the use of saturated diols is particularly preferred, and to this extent a process according to the invention is preferred, wherein the combined mass fraction of saturated diols is in the range from 50 to 99%, preferably in the range from 60 to 97%, particularly preferably in the range from 70 to 95%, based on the mass of the starting composition.

[0068] Analogous to the above statements regarding polyisocyanates, higher-quality polyols can also be used to adjust the physicochemical properties of the starting composition. However, in the inventors' opinion, the resulting branching of the polyurethane prepolymers should be kept as low as possible in this case as well.In this respect, a process according to the invention is preferred, wherein the starting composition comprises one or more polyol compounds having three or more hydroxyl groups, preferably in a combined mass fraction of 30% or less, particularly preferably 15% or less, very particularly preferably 3% or less, extremely preferably 0.5% or less, based on the mass of the starting composition and / or wherein the combined mass fraction of polyol compounds having three or more hydroxyl groups in the starting composition is 10% or less, particularly preferably 5% or less, very particularly preferably 1% or less, based on the mass of the starting composition.

[0069] In the opinion of the inventors, polyester diols or polyether diols are particularly suitable for the second diol compounds, but sometimes also for the first diol compounds, since these result in crosslinked adhesives with advantageous adhesive properties. Accordingly, a process according to the invention is preferred, wherein the first diol compounds and / or the second diol compounds, preferably the second diol compounds, are selected from the group consisting of diols having one or more, preferably two or more, particularly preferably a plurality of, functional groups selected from the group consisting of ether groups and ester groups, preferably ester groups, and / or wherein the first diol compounds and / or the second diol compounds, preferably the second diol compounds, are selected from the group consisting of polyester diols and polyether diols, preferably polyester diols.

[0070] The inventors have identified it as particularly advantageous if hydroxy-modified polyterpenes, polybutadienediols, fatty acid-based polyesters, or castor oil-based polyesters, preferably hydroxy-modified polyterpenes, are also used in the starting composition. These compounds, in particular the so-called polyfarnesenes among the hydroxy-modified polyterpenes, result, in the inventors' estimation, in particularly advantageous damping properties. Corresponding compounds are known to the person skilled in the art. The following formula I) visualizes an exemplary diol having a backbone of polyfarnesenes.

[0071] Thus, a process according to the invention is preferred, wherein the starting composition comprises one or more polymeric diol compounds having a backbone of polymerized isoprene units and / or having a backbone of polyterpenes, preferably a backbone of polymerized farnesenes, preferably with a combined mass fraction in the range of 5 to 95%, particularly preferably in the range of 10 to 90%, most particularly preferably in the range of 15 to 80%, based on the mass of the starting composition.

[0072] To obtain a crosslinked adhesive composition that is advantageous in terms of sustainability, the inventors propose, also with regard to the diols used, that bio-based compounds can be used that are advantageously suitable for the process according to the invention and that can particularly preferably be combined with bio-based diisocyanates. A process according to the invention is preferred in which the first diol compounds and / or the second diol compounds, preferably the first diol compounds and the second diol compounds, are produced from renewable raw materials, wherein the production preferably comprises the conversion of plant biomass.

[0073] The inventors have succeeded in identifying an advantageous process for the production of polyurethane prepolymers, which can be carried out either in a solvent or solvent-free, with the former being preferred. When using solvents, a process according to the invention is preferred, wherein the one or more polyurethane prepolymers can be prepared by reacting the starting composition in a solvent, the solvent being selected from the group consisting of ketones, for example acetone or butan-2-one, esters, for example ethyl acetate, ethers, amides, hydrocarbons, for example gasoline 60 / 90, toluene, halogen-containing hydrocarbons, and mixtures of these solvents.

[0074] Regardless of the use of a solvent, preference is given to a process according to the invention wherein the one or more polyurethane prepolymers can be prepared by reacting the starting composition at a temperature in the range from 0 to 120 °C, preferably in the range from 10 to 100 °C, particularly preferably in the range from 20 to 80 °C.

[0075] For the preparation of the polyurethane prepolymers, it is, in the opinion of the inventors, expedient in many cases to provide a catalyst. An example of this is a process according to the invention, wherein the one or more polyurethane prepolymers can be prepared by reacting the

[0076] Starting composition in the presence of a catalyst, wherein the catalyst is selected from the group consisting of

[0077] Organobismuth compounds, organotin compounds, organozirconium compounds, organozinc compounds, tertiary amine compounds, morphine-containing compounds, iron-containing salts, and potassium-containing salts. For the crosslinking of the polyurethane prepolymers in process step b), both the radical mechanism and the Michael reaction of the thiol-ene reaction can be advantageously utilized, allowing a targeted adaptation of the crosslinking chemistry to the respective application requirements. Particularly advantageous pot lives and good extrudability are achieved through the radical mechanism, with the Michael reaction opening up applications in areas where the use of a radiation source for curing would be disadvantageous.

[0078] In the opinion of the inventors, therefore, a process according to the invention is initially preferred, wherein the crosslinking of the polyurethane prepolymers in the prepolymer composition is carried out at least partially, preferably predominantly, particularly preferably substantially exclusively, by radical reaction of CC double bonds of the first diol compounds with one or more multifunctional thiol compounds.

[0079] In this case, it is advantageous to use typical initiator systems known to those skilled in the art for radical crosslinking, such as those used, for example, in (meth)acrylate-based systems. According to the inventors, radiation-based curing is particularly advantageous, especially for applications in 3D printing. In this respect, a process according to the invention is preferred, wherein the one or more initiator compounds 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 respect, a process according to the invention is preferred, wherein the one or more initiator compounds are selected from the group consisting of α-hydroxyketones, α-alkoxyketones, α-aminoarylketones, diarylketones, azo compounds, acylphosphine oxides, organic or inorganic peroxides, camphorquinones, and camphorquinone derivatives. Additionally or alternatively, a process according to the invention is preferred, wherein the one or more initiator compounds are used in a combined mass fraction in the range from 0.001 to 5%, preferably in the range from 0.05 to 1%, based on the mass of the polyurethane prepolymers in the prepolymer composition. The person skilled in the art will also understand that these are processes according to the invention, wherein the prepolymer composition comprises the corresponding initiator compounds.

[0080] The inventors have identified temperature ranges at which particularly advantageous results can be achieved during crosslinking. When thermally activated initiators are used, a process according to the invention is preferred, wherein the crosslinking of the polyurethane prepolymers in the prepolymer composition takes place at a temperature in the range from 40 to 300°C, preferably in the range from 50 to 280°C, particularly preferably in the range from 60 to 150°C. Alternatively, when radiation-activated initiators are used, a process according to the invention is preferred, wherein the crosslinking of the polyurethane prepolymers in the prepolymer composition takes place at a temperature in the range from -10 to 40°C, preferably in the range from 10 to 30°C, particularly preferably in the range from 20 to 25°C.

[0081] In the opinion of the inventors, an alternative preferred method is a process according to the invention wherein the crosslinking of the polyurethane prepolymers in the prepolymer composition takes place at least partially, preferably predominantly, particularly preferably essentially exclusively, by reacting CC double bonds of the first diol compounds with one or more multifunctional thiol compounds in a Michael addition. For this purpose, a process according to the invention is preferred wherein the crosslinking of the polyurethane prepolymers in the prepolymer composition is catalyzed by one or more catalyst compounds, wherein the one or more catalyst compounds are selected from the group consisting of bases and nucleophilic compounds, preferably selected from the group consisting of nucleophilic compounds.Particularly preferred in this respect is a process according to the invention wherein 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, n-alkylamines, N,N-dimethylpyridine-4-amine or 1H-imidazole, and phosphorus-centered nucleophiles, such as trialkylphosphines and alkylaryl phosphines, such as methyldiphenylphosphine. With regard to the concentration of these catalyst compounds, preferred is a process according to the invention wherein the one or more catalyst compounds are used in a combined mass fraction in the range of 0.001 to 5%, preferably 0.1 to 1%, based on the mass of the polyurethane prepolymers in the prepolymer composition.It is also conceivable to use photocatalysts that can be activated by visible light and decompose into corresponding bases, for example isopropylthioxanthone in combination with triazabicyclodecenetetraphenylborate.

[0082] Although difunctional thiols can also be used, at least in part, as multifunctional thiol compounds, the inventors believe that it is preferable to use higher-functionality thiols to achieve advantageous degrees of crosslinking. Accordingly, a process according to the invention is preferred, wherein the one or more multifunctional thiol compounds are selected from the group consisting of thiol compounds with two or more, preferably three or more, particularly preferably two or three, and most particularly preferably three, thiol groups.

[0083] In this respect, the inventors have succeeded in identifying particularly advantageous thiol compounds and particularly suitable concentration ranges for their use. In this respect, a process according to the invention is preferred, wherein the one or more multifunctional thiol compounds are selected from the group consisting of ethylene glycol bis(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), trimethylolpropane tris(2-mercaptoacetate), ethylene glycol bismercaptoacetate, 1,1,1-tris(hydroxymethyl)propane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate), 2,2'-(ethylenedioxy)diethanethiol, tetra(ethylene glycol)dithiol, ethoxylated trimethylolpropane tri(3-mercaptopropionate) and

[0084] Polycaprolactone tetra(3-mercaptopropionate). Additionally or alternatively, a process according to the invention is preferred, wherein the one or more multifunctional thiol compounds are used in a combined mass fraction in the range of 0.5 to 10%, preferably 3 to 6%, based on the mass of the polyurethane prepolymers in the prepolymer composition. The skilled person will readily understand that these are processes according to the invention, wherein the prepolymer composition comprises the corresponding multifunctional thiol compounds and any initiators present.

[0085] With regard to the mass fractions defined above, however, it should be noted that these apply in the case where no reactive diluents are included in the prepolymer composition. These reactive diluents are preferably multifunctional olefins. In contrast to radical chain polymerizations, however, in the case of a thiol-ene reaction, the amount of multifunctional thiol compounds must also be increased when using reactive diluents.Preference is given to a process according to the invention wherein, upon crosslinking the polyurethane prepolymers in the prepolymer composition, there is at least partial reaction of CC double bonds of the first diol compounds with a multifunctional thiol compound and one or more unsaturated extender molecules, wherein the extender molecules are preferably selected from the group consisting of multifunctional olefins, for example difunctional olefins, preferably allyl and vinyl ethers. However, preference is given in this case to a process according to the invention wherein the one or more multifunctional thiol compounds are used in a combined mass fraction in the range of 0.5 to 40%, preferably 3 to 25%, based on the mass of the polyurethane prepolymers in the prepolymer composition.In this case, additionally or alternatively, a process according to the invention is preferred, wherein the one or more multifunctional thiol compounds are used in a combined mass fraction in the range of 0.5 to 30%, preferably 3 to 15%, based on the combined mass of the polyurethane prepolymers and the extender molecules in the prepolymer composition.

[0086] In the inventors' opinion, it is particularly advantageous if the produced crosslinked adhesive also comprises resins, in particular tackifier resins. In this respect, a process according to the invention is preferred, wherein the crosslinked adhesive comprises one or more resins, preferably in a combined mass fraction of 70% or less, more preferably 60% or less, and most preferably 50% or less, based on the mass of the crosslinked adhesive. Examples of such adhesive resins include hydrocarbon resins (for example 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 as well as rosin and its derivatives, for example disproportionated, dimerized or esterified resins, for example reaction products with glycol, glycerol or pentaerythritol.

[0087] However, the inventors have identified specific polyurethane-based resins as particularly suitable for the polyurethane-based crosslinked adhesives, which the inventors have specifically tailored to the requirements of the process according to the invention and which are considered particularly advantageous in connection with the use of 3D printing processes. A process according to the invention is particularly preferred, wherein the resins are selected from the group consisting of polyurethane resins. Of course, the polyurethane resins in question here are not the polyurethane prepolymers or the crosslinked polyurethane polymers of the process according to the invention; rather, the polyurethane resins are different from them. It is self-explanatory that the polyurethane resins are incorporated into or added to the crosslinked adhesive produced by the process according to the invention.

[0088] Particularly preferred is a process according to the invention, wherein the polyurethane resin can be prepared by reacting a resin starting composition comprising: i) one or more diisocyanate components, and ii) one or more polyol components, preferably diol components.

[0089] In this respect, the inventors have identified it as particularly advantageous if monomeric polyols and no oligomeric compounds are used in the corresponding resin starting composition, thereby achieving a high density of urethane groups. Therefore, a process according to the invention is preferred, wherein the polyol components have a weight-average molecular weight M wof 400 g / mol or less, preferably of 250 g / mol or less. Additionally or alternatively, a process according to the invention is also preferred wherein the combined mass fraction of oligomeric and polymeric polyol components is 10% or less, preferably 5% or less, particularly preferably 1% or less, very particularly preferably 0.1% or less, based on the mass of the starting resin composition. Accordingly, additionally or alternatively, a process according to the invention is also preferred wherein the polyol components are monomeric polyol components.

[0090] Also preferred is a process according to the invention wherein the polyol components are not first diol compounds. Particularly preferred in this respect is a process according to the invention wherein the polyol components do not comprise any terminal CC double bonds, preferably none at all.

[0091] A process according to the invention is preferred, wherein the resin, preferably the polyurethane resin, has a weight-average molecular weight M w measured by GPC in the range of 300 to 4000 g / mol, preferably in the range of 500 to 1500 g / mol. Additionally or alternatively, a process according to the invention is also preferred, wherein the resin, preferably the polyurethane resin, has a glass transition temperature measured by DSC of -20°C or more, preferably 0°C or more. Additionally or alternatively, a process according to the invention is also preferred, wherein the resin, preferably the polyurethane resin, is semicrystalline or amorphous.

[0092] With regard to the selection of the diisocyanate components, a process according to the invention is preferred, wherein the one or more diisocyanate components are selected from the group consisting of hexamethylene diisocyanate, 1,6-diisocyanato-2,2,4-trimethylhexane,

[0093] 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, naphthylene-1,5-diisocyanate and meta-tetramethylxylylene diisocyanate, preferably selected from the group consisting of hexamethylene diisocyanate, 1,6-diisocyanato-2,2,4-trimethylhexane,

[0094] 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). To obtain a polyurethane resin with good biodegradability, which is excellently suited for combination with appropriately designed crosslinked polyurethanes, the inventors believe that processes according to the invention are particularly preferred, wherein the one or more diisocyanate components 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.With regard to the polyol components, a process according to the invention is preferred, wherein the 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.

[0095] With regard to the specific composition of the starting resin composition, a process according to the invention is preferred, wherein the starting resin composition comprises the one or more diisocyanate components in a combined mass fraction in the range from 30 to 70%, preferably in the range from 40 to 60%, particularly preferably in the range from 45 to 55%, based on the mass of the starting resin composition. In this respect, additionally or alternatively, a process according to the invention is preferred, wherein the starting resin composition comprises the one or more polyol components in a combined mass fraction in the range from 30 to 70%, preferably in the range from 40 to 60%, particularly preferably in the range from 45 to 55%, based on the mass of the starting resin composition.

[0096] According to the inventors' assessment, advantages also arise for the preferably used polyurethane resins, analogous to the above statements, if monofunctional alcohols or isocyanates are used in the resin starting composition in addition to the diols and diisocyanates. Accordingly, a process according to the invention is preferred, wherein the resin starting composition comprises one or more monofunctional compounds which are selected from the group consisting of monofunctional alcohols and monofunctional isocyanates, preferably in a combined mass fraction of 10% or more, preferably 15% or more, particularly preferably 20% or more, based on the mass of the resin starting composition and / or in a combined amount of substance in the range from 0.5*[B] to 1.5*[B], preferably in the range from 0.8*[B] to 1.2*[B], particularly preferably in the range from 0.95*[B] to 1.05*[B], where [B] is the combined amount of substance of the terminal OH groups orIsocyanate groups of the polyurethane resins, where [B] can be determined, for example, by measurement on reference samples or estimated using typical simulation methods to adjust this feature.

[0097] It can be seen as an advantage of the process according to the invention that, in addition to resins and in particular polyurethane resins, it is also open to the presence of further constituents which can be added to the prepolymer composition and are accordingly contained in the crosslinked adhesive. This advantageously allows the physicochemical properties of the crosslinked adhesive to be specifically adapted to the respective application requirements. An example of this is a process according to the invention wherein the crosslinked adhesive comprises one or more further constituents, wherein the further constituents are selected from the group consisting of rheology additives, stabilizers, antioxidants and dyes, wherein the combined mass fraction of the further constituents is preferably in the range from 0.1 to 30%, preferably in the range from 0.5 to 20%, particularly preferably in the range from 1 to 20%, based on the mass of the crosslinked adhesive.

[0098] With regard to the subsequent handling of the crosslinked adhesive, it is particularly preferred to implement it as a pressure-sensitive adhesive, which can be achieved in particular by adding resins, very particularly preferably the polyurethane resins disclosed above. Accordingly, a process according to the invention is preferred in which the crosslinked adhesive is a pressure-sensitive adhesive.

[0099] In accordance with expert understanding, a pressure-sensitive adhesive is an adhesive that possesses pressure-sensitive adhesive properties, i.e., the ability to form a permanent bond with a substrate even under relatively light pressure. Such pressure-sensitive adhesive tapes can usually be removed from the substrate after use without leaving any residue and are generally permanently tacky even at room temperature, meaning they exhibit a certain viscosity and initial tackiness, allowing them to wet the surface of a substrate even under light pressure. The tackiness of a pressure-sensitive adhesive tape results from the fact that a pressure-sensitive adhesive is used as the adhesive.Without wishing to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to the permanent inherent tack and pressure-sensitive adhesive capacity described above. It is assumed that with corresponding pressure-sensitive adhesives, mechanical deformation leads to both viscous flow processes and the build-up of elastic restoring forces. The partial viscous flow serves to achieve adhesion, while the partial elastic restoring forces are necessary in particular to achieve cohesion. The relationships between rheology and pressure-sensitive tack are known in the art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition, (1999), pages 153 to 203.To characterise the degree of elastic and viscous components, the storage modulus (G') and the loss modulus (G") are usually used, which can be determined by means of dynamic mechanical analysis (DMA), for example using a rheometer, as disclosed, for example, in WO 2015 / 189323. In the context of the present invention, an adhesive is preferably understood to be pressure-sensitive and thus a pressure-sensitive adhesive if, at a temperature of 23°C in the deformation frequency range from 10° to 10. 1 rad / sec G' and G“ each at least partly in the range of 10 3 up to 10 7Pa. A special case of the further components which serve to adjust the properties of crosslinked adhesives are insoluble fillers which can be added to the prepolymer composition in order to obtain a filled crosslinked adhesive after crosslinking. These are, for example, particulate fillers with an average particle diameter (D50) of 5 μm or more, preferably 10 μm or more, particularly preferably 20 μm or more, which are insoluble in the prepolymer composition and are accordingly present therein as a dispersion, or macroscopic fillers, such as, for example, fibers. The insoluble fillers are preferably selected from the group consisting of particulate fillers.Particularly preferably, the insoluble fillers are selected from the group consisting of 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, scrims, platelets, and rods made of materials insoluble in the prepolymer composition are also suitable as insoluble fillers. Due to their sometimes already macroscopic dimensions and their lack of solubility, these generally have no significant influence on the relationships between the prepolymer composition and the crosslinking chemistry disclosed above.Accordingly, these insoluble fillers are not attributed to the prepolymer composition within the scope of the present invention and are accordingly not taken into account when calculating mass fractions relative to the mass of the prepolymer composition. Rather, within the scope of the present invention, it is defined that the addition of insoluble fillers to a prepolymer composition results in a filled prepolymer composition. In this case, this is therefore a process according to the invention, wherein the prepolymer composition is a filled prepolymer composition consisting of: aa.1) the prepolymer composition, and aa.2) one or more insoluble fillers, wherein the combined mass fraction of the insoluble fillers is preferably in the range from 0.1 to 20%, particularly preferably in the range from 0.5 to 15%, very particularly preferably in the range from 1 to 10%, based on the mass of the prepolymer composition.

[0100] The process according to the invention can be advantageously used not only for the production of adhesive tapes, but also in 3D printing processes to create more complex three-dimensional adhesive structures. Nevertheless, the production of adhesive tapes is of great industrial importance.

[0101] The invention thus initially also relates to a process for producing an adhesive tape, comprising the process steps of the process according to the invention for producing a crosslinked adhesive, and before or during, preferably before, process step b) the process step: b1 a) forming a prepolymer layer from the prepolymer composition on a carrier layer or a release layer.

[0102] The term "adhesive tape" is clear to those skilled in the field of adhesive technology. Within the scope of the present invention, the term "tape" refers to all thin, flat structures, i.e., structures with a predominantly two-dimensional extension, in particular films, film sections, and labels, preferably tapes with an extended length and a limited width, as well as corresponding tape sections.

[0103] The coating thickness of the prepolymer composition is preferably in the range of 10 to 1000 g / m 2 , preferably in the range of 15 to 500 g / m 2 , particularly preferably in the range of 20 to 100 g / m 2 .

[0104] With a view to the most favorable handling properties possible, particularly advantageous results are regularly achieved when crosslinked adhesive compositions according to the invention are used as the adhesive layer of a single- or double-sided adhesive tape that also comprises a carrier layer, or when the adhesive layer is arranged on a release layer, for example a liner, from which the adhesive layer can be easily removed. In this respect, a method for producing an adhesive tape in which the prepolymer layer is formed on a release layer is particularly preferred.Preferred is a method for producing an adhesive tape, wherein the release layer comprises one or more materials selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, paper and combinations of these materials, wherein the release material is preferably coated on one or both sides, particularly preferably on both sides, with a release layer, preferably a carbamate or silicone release layer, particularly preferably a silicone release layer, wherein the silicone release layer can most preferably be produced by crosslinking a crosslinkable silicone system comprising one or more polysiloxanes.

[0105] The term "backing layer," in contrast to the release layer, usually refers to the layer of a multilayer adhesive tape that largely determines the mechanical and physical properties of the tape, such as tear resistance, stretchability, insulation, or resilience. Common materials for the backing layer include fabric, scrims, paper, and plastic films, such as PET and polyolefin films.

[0106] When using carrier layers, it is often advantageous to use an adhesion promoter, a so-called primer layer, between the carrier material and the prepolymer composition, or to perform a physical pretreatment of the carrier surface to improve the adhesion of the crosslinked adhesive to the carrier material. In adhesive tapes according to the invention with a carrier layer, the adhesive layers can in turn be covered with a release liner to enable problem-free unwinding and to protect the adhesive from contamination. In the case of single-sided adhesive tapes, the carrier can be coated on one side with a release layer, which can be based, for example, on silicone, carbamate, or acrylate.

[0107] However, due to the specific suitability of the method according to the invention for use in 3D printing processes, the invention also relates in particular to a method for producing a crosslinked three-dimensional adhesive structure in a 3D printing process, comprising the method steps of the method according to the invention for producing a crosslinked adhesive mass, and before or during, preferably before, method step b), the method step: b1 b) shaping the prepolymer composition with the dispensing unit of a 3D printing device for producing a three-dimensional adhesive structure.

[0108] A person skilled in the art is familiar with a variety of methods for producing three-dimensional target structures using 3D printing devices, in particular so-called material extrusion methods. Those skilled in the art will understand that the method according to the invention is fundamentally compatible with various 3D printing devices and 3D printing methods. In this respect, a method for producing a three-dimensional adhesive structure is preferred, wherein the three-dimensional adhesive structure is produced using a melt coating process.

[0109] Such a 3D printing process initially comprises, method-independently, the creation of a three-dimensional adhesive structure from the prepolymer composition, which is crosslinked in process step b) in order to obtain a crosslinked three-dimensional adhesive structure.

[0110] The inventors propose that the viscosity of the prepolymer composition, or its temperature dependence, should be specifically optimized when implementing a corresponding 3D printing process in order to obtain particularly advantageous application properties, in which the prepolymer composition can be applied easily and precisely, but at the same time displays sufficient structural integrity to form a three-dimensional adhesive structure and maintain this shape until crosslinking. The inventors have succeeded in identifying particularly preferred viscosity ranges that can be adjusted to obtain prepolymer compositions that are excellently suited for use in various 3D printing processes, in particular melt coating processes. Preference is given to a process according to the invention wherein the prepolymer composition has a dynamic viscosity in the range of 500 to 500,000 Pa s, preferably in the range of 1,000 to 200,000 Pa s at 25°C.000 Pa s, particularly preferably in the range from 2000 to 100,000 Pa s. Additionally or alternatively, a process according to the invention is preferred, wherein the prepolymer composition at 100 °C has a dynamic viscosity in the range from 2 to 2500 Pa s, preferably in the range from 5 to 2000 Pa s, particularly preferably in the range from 10 to 1000 Pa s, very particularly preferably in the range from 15 to 300 Pa s. In the context of the present invention, the dynamic viscosity is determined according to DIN 53019-1 from 2008; at the respective temperature, with a shear rate of 1 s. -1 certainly.

[0111] The person skilled in the art will understand that the invention also relates to a crosslinked adhesive which is produced or can be produced using a process according to the invention for producing a crosslinked adhesive.

[0112] Based on the method according to the invention for producing an adhesive tape or for producing a three-dimensional adhesive structure, the products obtained thereby are also disclosed within the scope of the invention.

[0113] Accordingly, an adhesive tape is first disclosed, produced or producible by the method according to the invention for producing an adhesive tape, comprising an adhesive layer comprising a crosslinked adhesive composition according to the invention, wherein the adhesive layer is arranged on a carrier layer or a release layer.

[0114] Also disclosed is a crosslinked three-dimensional adhesive structure produced or producible by the method according to the invention for producing a three-dimensional adhesive structure, comprising a three-dimensionally shaped crosslinked adhesive composition according to the invention.

[0115] Finally, the use of a prepolymer composition as disclosed above, ie a

[0116] A prepolymer composition comprising one or more polyurethane prepolymers, wherein the one or more polyurethane prepolymers are preparable by reacting a starting composition comprising: iv) one or more diisocyanate compounds, 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 CC double bond per molecule, and iii.v) one or more second diol compounds different from the first diol compounds, as a printing substance in a 3D printing process, in particular a melt coating process, for producing a three-dimensional adhesive structure, preferably in a process according to the invention for producing a crosslinked three-dimensional adhesive structure. The invention and preferred embodiments of the invention are further explained and described below with reference to experiments.

[0117] The substances used are listed in Table 1 below.

[0118] Table 1 - Substances used

[0119]

[0120] The samples produced within the scope of the invention were tested using the following methods. Unless otherwise stated, measurements were performed at a test temperature of 23 ± 1 °C and 50 ± 5% relative humidity. Glass transition temperature (DSC):

[0121] The glass transition temperature (Tg) was determined using differential scanning calorimetry (DSC). Approximately 5 mg of the sample was weighed into an aluminum crucible (volume 25 pL) and sealed with a perforated lid. The measurement was carried out using a Netzsch DSC Sirius 3500 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, heating was again carried out at 10 K / min to 150 °C. The change in heat capacity was recorded, allowing glass transitions to be identified as steps in the diagram. The glass transition temperature was evaluated in the usual way: A tangent was drawn to the baseline of the thermogram before and after the step.In the step area, a best-fit line is placed parallel to the ordinate so that it intersects the two tangents, creating two areas of equal area (between the tangent, the best-fit line, and the measured curve). The intersection point of the best-fit line positioned in this way with the measured curve indicates the glass transition temperature.

[0122] Adhesive strength:

[0123] The adhesive strength (peel strength) test is performed in accordance with PSTC-1. A 2 cm wide strip of pressure-sensitive adhesive tape, consisting of a 23 μm thick PET film etched with trichloroacetic acid and the pressure-sensitive adhesive film applied to it, is bonded to the test panel by rolling over it five times using a 4 kg roller. The test panel is clamped in place, and the self-adhesive strip is peeled off via its free end using a tensile testing machine at a peel angle of 180° and a speed of 300 mm / min. The required force is determined using a tensile testing device. The measurement results are averaged over three measurements and standardized to the width of the strip in N / cm. The test panels are polished steel panels with a thickness of 2 mm.

[0124] Shear strength: The shear strength test is performed according to PSTC-7. A 1.3 cm wide strip of self-adhesive tape is bonded to a polished steel plate over a length of 2 cm using a 2 kg roller by rolling it over twice. The plates are equilibrated for 30 minutes under test conditions but without load. The test weight is then suspended, creating a shear stress parallel to the bond surface, and the time in minutes until the bond fails is measured. If a holding time of 10,000 min is reached, the test is terminated before the bond fails.

[0125] Disintegration behavior:

[0126] Based on DIN EN ISO 20200:2016-05, the disintegration behavior of the polymers was tested in the laboratory under simulated composting conditions as a measure of compostability. Disintegration describes the physical decomposition of a material into very small fragments. To pass the test, at least 90% must decompose into particles < 2 mm within 6 months. Commercially available compost soil is used for the disintegration test, in this case the compost soil with the brand name tangocomp from VKN-Vertriebsgesellschaft Kompostprodukte Nord mbH. The moisture content of the compost soil is adjusted to 55 to 60%. To determine the moisture content, three 10 g samples of compost soil are dried for 2 hours at 120 °C, and then the moisture loss and thus the water content of the soil are determined. Any missing moisture is replenished with non-chlorinated tap water.

[0127] For the disintegration test, 150 g of compost adjusted to a moisture content of 60% is weighed into a 1000 mL PE beaker. A 25 cm thick layer of compost is then placed on top of this first layer of soil. 2 large piece of the sample to be tested. The sample is the adhesive mass (layer thickness: 200 μm) which is coated for this test onto a cellophane film (a carrier material with known degradation behavior) with a layer thickness of 25 μm. A second layer of compost soil, also weighing 150 g, is placed on top of the sample. The PE cup is closed with a lid. For ventilation of the compost, the lid is previously provided with two holes with a diameter of 2.0 mm each. The sample prepared in this way is stored at 60 ± 2 °C for a maximum of 180 days and the water loss is recorded every 3 to

[0128] The decomposition is balanced by adding water for 4 days. The progress of decomposition of the samples is assessed by visual inspection after a period of 12 weeks.

[0129] The disintegration behavior was assessed qualitatively for all samples. The results were then categorized based on the degree of decomposition after 12 weeks as follows:

[0130] (+) Sample > 90% decomposed into particles < 2 mm;

[0131] (o) Sample decomposed to 50 - 90% into particles < 2 mm; and

[0132] (-) Sample decomposed to < 50% into particles < 2mm.

[0133] Shock resistance (DuPont test)

[0134] For the impact resistance test, transfer tapes were produced, each with a pressure-sensitive adhesive film thickness of 50 μm. The sample was cut into a square, frame-shaped geometry using a laser cutter (outer width: 33 mm x 33 mm; web width: 2 mm; inner dimensions (window cutout): 29 mm x 29 mm). The sample was then bonded to a polycarbonate (PC) window (35 mm x 35 mm, thickness: 3 mm). A polycarbonate frame (outer width: 45 mm x 45 mm; web width: 10 mm; inner dimensions (window cutout): 25 mm x 25 mm; thickness: 3 mm) was bonded to the other side of the transfer tape. The bonded area was 248 mm. 2 The bonding is carried out in such a way that the geometric centers and the diagonals are aligned (corner to corner). The bonding is then carried out for

[0135] 5 s with 248 N and stored for 24 h.

[0136] The assembly consisting of PC frame, adhesive tape, and PC window is clamped into a sample holder so that the protruding edges of the frame lie flat. The assembly is aligned horizontally. The window is attached below the PC frame, held in place only by the adhesive bond (“free floating”). The sample holder is then inserted into the designated frame of the “DuPont Impact Tester.” The impact head (weight: 150 g) is inserted so that the circular impact geometry with a diameter of 24 mm lies centrally and flush with the surface of the PC window, which is freely accessible from above. A weight guided by two guide rods is dropped vertically from a height of 5 cm. The height of the dropping weight is increased in 5 cm increments until the adhesive bond is broken by the applied impact energy and the PC window detaches from the PC frame. Five measurements are taken per sample, and the average value is then determined.

[0137] For the comparability of different samples, the energy (E) is calculated as follows: E [J] = Height [m] * Mass Weight [kg] * 9.81 kg / m*s 2 .

[0138] A. Production of polyurethane prepolymers:

[0139] The polyurethane prepolymers are produced in a solvent-based manner using the components listed in Table 2. Alternatively, the polyurethane prepolymers can also be produced solvent-free.

[0140] The polyurethane prepolymer was prepared by weighing the solvent and all first and second diol compounds, as well as any additional polyols and the catalyst, into a reaction vessel. The mixture was homogenized using a mechanical laboratory stirrer under an inert gas atmosphere. The diisocyanate(s) were added, and the mixture was stirred for 1.5 h at room temperature under an inert gas atmosphere. The mixture was then stored in an oven at 40 °C for 48 h to complete the reaction.

[0141] Table 2 - Preparation of polyurethane prepolymer

[0142] B. Production of adhesives:

[0143] Crosslinked adhesives were prepared from the polyurethane prepolymers prepared under point A. The initiator and the multifunctional thiol compounds according to Table 3 were added to the polyurethane prepolymer, and the mixture was homogenized for at least 5 minutes. To produce an adhesive tape, the mixture was coated onto a carrier made of etched PET film or a silicone-release-coated PET liner using a laboratory spreader. The solvent was evaporated in a forced-air oven at 80 °C (etched PET film) or 60 °C (silicone-release-coated PET liner) for 15 minutes. The dried films were covered with siliconized PET film. In the case of photoinitiators, the uncrosslinked films were treated with a UV source matched to the initiator (dose: 1800-2400 mJ / cm 2). Pressure-sensitive adhesive crosslinked films with a layer thickness of 25-30 pm (unless otherwise stated) were obtained. In principle, however, crosslinking can also be achieved via the thiol-Michael reaction. Crosslinking of the reference PSA13 was conventionally achieved using a polyisocyanate.

[0144] Table 3 - Production of crosslinked adhesives a) For PSA10, the siliconized PET film was removed before crosslinking to realize crosslinking under the influence of oxygen.

[0145] The adhesive tapes produced according to points A and B were tested for their properties using the methods described above. The results are summarized in Table 4. Table 4 - Test results

[0146] The test results listed in Table 4 demonstrate that the process according to the invention, using an alternative crosslinking chemistry, can be used to obtain advantageous pressure-sensitive adhesives that can be tailored to the various application requirements of the skilled person. In particular, advantageous bond strengths, shear life, and impact resistance can be achieved in this way. Furthermore, the process according to the invention makes it possible to obtain pressure-sensitive adhesives that exhibit advantageous disintegration behavior. The pressure-sensitive adhesives with the advantageous property profiles can be obtained in an advantageous manner without the disadvantages of the crosslinking processes known from the prior art becoming apparent during production, and in particular, the risk of exposure to or release of isocyanate compounds is also minimized.The corresponding manufacturing processes are very robust against changing environmental conditions and very tolerant of the presence of additives that could interact with OH or isocyanate groups. Thanks to the possibility of radiation activation, manufacturing is very reliable, time-efficient, and cost-effective. Furthermore, the comparison between PSA9 and PSA10 shows that, advantageously, no negative influence can be detected even during crosslinking under the influence of oxygen, further demonstrating the advantageous robustness of the process according to the invention. This is an advantage, particularly compared to processes known from the prior art, but also compared to processes based on a direct radical conversion of terminal CC double bonds.

[0147] D. Production of polyurethane resins:

[0148] Advantageous polyurethane resins were prepared from the components listed in Table 5 for use in the crosslinked adhesives of the present invention. The polyurethane resin was prepared in each case by weighing the solvent, all polyol components, and the catalyst into a reaction vessel (although, alternatively, solvent-free preparation would also be possible). The mixture was homogenized using a mechanical laboratory stirrer under an inert gas atmosphere. The diisocyanate component was added, and the mixture was stirred for 1.5 h at room temperature under an inert gas atmosphere. The mixture was then stored in an oven at 40°C for 48 h to complete the reaction. The resulting polyurethane resins can be used both in solution and in solvent-free form.

[0149] Table 5 - Production of polyurethane resins

[0150] Based on experiments by the inventors with non-inventive crosslinked pressure-sensitive adhesives which were directly crosslinked radically via the first diol compounds, excellent adhesive properties, in particular advantageous finger tack and good adhesive strengths, can be expected with the specific polyurethane resins in combination with the crosslinked adhesives prepared according to the invention, without impairing the degradation behavior, in particular in comparison to established resins such as terpene-phenolic resins or hydrogenated rosin resins.

[0151] E. 3D printing of adhesives:

[0152] Based on experiments by the inventors with non-inventive crosslinked pressure-sensitive adhesives, which were directly crosslinked radically via the first diol compounds, it has been shown that the specific polyurethane prepolymers and the crosslinking chemistry controlled via the first diol compounds allow for excellent suitability for use in 3D printing.

[0153] In this experiment, a corresponding polyurethane prepolymer was produced solvent-free and transferred into a print cartridge without bubbles. The 3D printing experiment was successfully carried out using an InnovatiQ X400 printer. Printing was carried out at a feed temperature of 90 °C, thus ensuring an extrusion temperature of at least 70 °C. With a pressure of 2.5 bar, the required circular geometry was printed onto a plastic plate through a 0.4 mm wide nozzle operating according to the endless piston principle. The previously uncured adhesive was cured with a UV source matched to the initiator (dose: 1800-2400 mJ / cm 2 ) to crosslink the adhesive in the previously created geometry.

Claims

Claims 1. A process for producing a crosslinked adhesive, in particular within the framework of a 3D printing process, comprising the process steps: a) producing a prepolymer composition comprising one or more polyurethane prepolymers, wherein the one or more polyurethane prepolymers can be produced by reacting a starting composition comprising: i) one or more diisocyanate compounds, ii) one or more first diol compounds, wherein the first diol compounds are selected from the group consisting of diols having at least one CC double bond per molecule, and iii) one or more second diol compounds different from the first diol compounds, and b) crosslinking the polyurethane prepolymers in the prepolymer composition by reacting CC double bonds of the first diol compounds with one or more multifunctional thiol compounds, to obtain crosslinked polyurethane polymers.

2. The process of claim 1, wherein the starting composition comprises the one or more diisocyanate compounds in a combined mass fraction in the range of 1 to 30%, based on the mass of the starting composition.

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

4. A process according to any one of claims 1 to 3, wherein the starting composition comprises the one or more first diol- Compounds in a combined mass fraction in the range of 0.05 to 20%, based on the mass of the starting composition.

5. The process according to any one of claims 1 to 4, wherein the second diol compounds are selected from the group consisting of diols having a weight-average molecular weight Mw measured by GPC in the range of 200 to 6000 g / mol.

6. The process according to any one of claims 1 to 5, wherein the second diol compounds are selected from the group consisting of diols having a backbone of polymerized isoprene units and / or having a backbone of polyterpenes.

7. A process according to any one of claims 1 to 6, wherein the starting composition comprises the one or more second diol compounds in a combined mass fraction in the range of 50 to 95%, based on the mass of the starting composition.

8. The process according to any one of claims 1 to 7, wherein the crosslinking of the polyurethane prepolymers in the prepolymer composition is carried out at least partially by radical reaction of CC double bonds of the first diol compounds with one or more multifunctional thiol compounds.

9. A process according to any one of claims 1 to 8, wherein the crosslinking of the polyurethane prepolymers in the prepolymer composition is carried out at least partially by reacting CC double bonds of the first diol compounds with one or more multifunctional thiol compounds in a Michael addition.

10. The method according to any one of claims 1 to 9, wherein the crosslinked adhesive comprises one or more resins, wherein 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 at 25 °C in the range of 500 to 500,000 Pa*s, and / or wherein 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 adhesive is a pressure-sensitive adhesive.

13. A method for producing an adhesive tape, comprising the method steps of the method according to any one of claims 1 to 12, and before or during method step b) the method step: bla) forming a prepolymer layer from the prepolymer composition on a carrier layer or a release layer.

14. A method for producing a cross-linked three-dimensional adhesive structure in a 3D printing method, comprising the method steps of the method according to any one of claims 1 to 12, and before or during method step b) the method step: b1 b) shaping the prepolymer composition with the dispensing unit of a 3D printing device to produce a three-dimensional adhesive structure.

15. Crosslinked adhesive, produced or producible by a process according to any one of claims 1 to 14.

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